Fix incorrect documentation for extended templates (#7068)
Fix incorrect documentation for extended templates (#7068)

Extended templates are loaded by including a `<script>` tag with a `custom-template` attribute rather than a `custom-element` attribute.
yieldmo/amphtml,pedjoni8/amphtml,kamtschatka/amphtml,smartadserver/amphtml,chaveznvg/amphtml,shawnbuso/amphtml,laterpay/amphtml,koshka/amphtml,pietergreyling/amphtml,yieldbot/amphtml,jpettitt/amphtml,ampproject/amphtml,nexxtv/amphtml,sortable/amphtml,media-net/amphtml,sharethrough/amphtml,yieldmo/amphtml,kmh287/amphtml,alanorozco/amphtml,ADITION/amphtml,zhucl/amphtml,Gregable/amphtml,ampproject/amphtml,sriramkrish85/amphtml,powdercloud/amphtml,sharethrough/amphtml,avimehta/amphtml,danielrozenberg/amphtml,Mobusi-ads/amphtml,bpaduch/amphtml,sharethrough/amphtml,luciancrasovan/amphtml,adiant/amphtml,yieldmo/amphtml,dotandads/amphtml,cory-work/amphtml,jdelhommeau/amphtml,chaveznvg/amphtml,mhc-gh/amphtml,Adtoma/amphtml,rsimha-amp/amphtml,zhangsu/amphtml,voyagegroup/amphtml,tlong2/amphtml,jdelhommeau/amphtml,erwinmombay/amphtml,arealit/amphtml,zhangsu/amphtml,pietergreyling/amphtml,bpaduch/amphtml,taboola/amphtml,spotxchange/amphtml,sebastianbenz/amphtml,prateekbh/amphtml,Gregable/amphtml,adiant/amphtml,widespace-os/amphtml,wjfang/amphtml,adiant/amphtml,jpettitt/amphtml,burtcorp/amphtml,zhouyx/amphtml,ecoron/amphtml,rlugojr/amphtml,kmh287/amphtml,sriramkrish85/amphtml,donttrustthisbot/amphtml,dotandads/amphtml,Gregable/amphtml,media-net/amphtml,Mobusi-ads/amphtml,sklobovskaya/amphtml,Mobusi-ads/amphtml,wjfang/amphtml,koshka/amphtml,jdelhommeau/amphtml,laterpay/amphtml,media-net/amphtml,lannka/amphtml,zhangsu/amphtml,yandex-pcode/amphtml,ADITION/amphtml,yieldbot/amphtml,fullspeed-sp/amphtml,clawr/amphtml,lzanol/amphtml,zhouyx/amphtml,wjfang/amphtml,zhouyx/amphtml,taboola/amphtml,tlong2/amphtml,src-code/amphtml,JuliusThms/amphtml,fullspeed-sp/amphtml,cvializ/amphtml,ADITION/amphtml,yieldmo/amphtml,vmarteev/amphtml,keithwrightbos/amphtml,vmarteev/amphtml,yieldmo/amphtml,vmarteev/amphtml,JuliusThms/amphtml,widespace-os/amphtml,alanorozco/amphtml,jpettitt/amphtml,luciancrasovan/amphtml,kmh287/amphtml,gumgum/amphtml,comScore/amphtml,yieldbot/amphtml,danielrozenberg/amphtml,rajkumarsrk/amphtml,jpettitt/amphtml,koshka/amphtml,cvializ/amphtml,Mobusi-ads/amphtml,Gregable/amphtml,comScore/amphtml,kmh287/amphtml,jpettitt/amphtml,sortable/amphtml,kixer-com/amphtml,adiant/amphtml,bpaduch/amphtml,src-code/amphtml,adiant/amphtml,jpettitt/amphtml,media-net/amphtml,DAC-f1h-dev/amphtml,kixer-com/amphtml,vmarteev/amphtml,jdelhommeau/amphtml,wjfang/amphtml,danielrozenberg/amphtml,yieldbot/amphtml,burtcorp/amphtml,donttrustthisbot/amphtml,zhucl/amphtml,erwinmombay/amphtml,comScore/amphtml,donttrustthisbot/amphtml,alanorozco/amphtml,DistroScale/amphtml,BenDz/amphtml,prateekbh/amphtml,ampproject/amphtml,cory-work/amphtml,lzanol/amphtml,kmh287/amphtml,rajkumarsrk/amphtml,fullspeed-sp/amphtml,fullspeed-sp/amphtml,donttrustthisbot/amphtml,comScore/amphtml,mhc-gh/amphtml,clawr/amphtml,adup-tech/amphtml,smartadserver/amphtml,media-net/amphtml,prateekbh/amphtml,sharethrough/amphtml,erwinmombay/amphtml,DarXector/amphtml,arealit/amphtml,cory-work/amphtml,sklobovskaya/amphtml,DarXector/amphtml,Mobusi-ads/amphtml,aghassemi/amphtml,camelburrito/amphtml,laterpay/amphtml,aghassemi/amphtml,camelburrito/amphtml,rsimha-amp/amphtml,rsimha-amp/amphtml,jmadler/amphtml,voyagegroup/amphtml,cory-work/amphtml,cory-work/amphtml,nexxtv/amphtml,rajkumarsrk/amphtml,aghassemi/amphtml,honeybadgerdontcare/amphtml,nexxtv/amphtml,yandex-pcode/amphtml,cvializ/amphtml,voyagegroup/amphtml,honeybadgerdontcare/amphtml,adup-tech/amphtml,techhtml/amphtml,lannka/amphtml,danielrozenberg/amphtml,avimehta/amphtml,mhc-gh/amphtml,honeybadgerdontcare/amphtml,ampproject/amphtml,rajkumarsrk/amphtml,engtat/amphtml,src-code/amphtml,Adtoma/amphtml,clawr/amphtml,zhucl/amphtml,yandex-pcode/amphtml,kamtschatka/amphtml,keithwrightbos/amphtml,camelburrito/amphtml,kamtschatka/amphtml,sebastianbenz/amphtml,honeybadgerdontcare/amphtml,bpaduch/amphtml,zhucl/amphtml,jmadler/amphtml,jridgewell/amphtml,erwinmombay/amphtml,yieldbot/amphtml,ecoron/amphtml,wjfang/amphtml,danielrozenberg/amphtml,BenDz/amphtml,sklobovskaya/amphtml,DarXector/amphtml,sebastianbenz/amphtml,powdercloud/amphtml,jridgewell/amphtml,smartadserver/amphtml,sharethrough/amphtml,JuliusThms/amphtml,mhc-gh/amphtml,keithwrightbos/amphtml,DistroScale/amphtml,burtcorp/amphtml,BenDz/amphtml,rlugojr/amphtml,pietergreyling/amphtml,pedjoni8/amphtml,media-net/amphtml,DAC-f1h-dev/amphtml,Gregable/amphtml,engtat/amphtml,widespace-os/amphtml,alanorozco/amphtml,powdercloud/amphtml,adup-tech/amphtml,yandex-pcode/amphtml,zhouyx/amphtml,zhouyx/amphtml,taboola/amphtml,media-net/amphtml,cvializ/amphtml,pietergreyling/amphtml,vmarteev/amphtml,techhtml/amphtml,smartadserver/amphtml,luciancrasovan/amphtml,avimehta/amphtml,rsimha-amp/amphtml,keithwrightbos/amphtml,kixer-com/amphtml,powdercloud/amphtml,jridgewell/amphtml,spotxchange/amphtml,alanorozco/amphtml,zhucl/amphtml,luciancrasovan/amphtml,yieldmo/amphtml,koshka/amphtml,nexxtv/amphtml,ecoron/amphtml,camelburrito/amphtml,bpaduch/amphtml,rlugojr/amphtml,rajkumarsrk/amphtml,vmarteev/amphtml,yandex-pcode/amphtml,danielrozenberg/amphtml,sriramkrish85/amphtml,clawr/amphtml,kixer-com/amphtml,DistroScale/amphtml,voyagegroup/amphtml,gumgum/amphtml,powdercloud/amphtml,zhouyx/amphtml,wjfang/amphtml,jridgewell/amphtml,rlugojr/amphtml,comScore/amphtml,clawr/amphtml,kmh287/amphtml,laterpay/amphtml,rlugojr/amphtml,jridgewell/amphtml,donttrustthisbot/amphtml,mhc-gh/amphtml,honeybadgerdontcare/amphtml,koshka/amphtml,camelburrito/amphtml,rsimha-amp/amphtml,erwinmombay/amphtml,spotxchange/amphtml,tlong2/amphtml,clawr/amphtml,techhtml/amphtml,jdelhommeau/amphtml,comScore/amphtml,jmadler/amphtml,vmarteev/amphtml,sklobovskaya/amphtml,DAC-f1h-dev/amphtml,nexxtv/amphtml,prateekbh/amphtml,arealit/amphtml,widespace-os/amphtml,zhucl/amphtml,dotandads/amphtml,lannka/amphtml,luciancrasovan/amphtml,voyagegroup/amphtml,ampproject/amphtml,engtat/amphtml,engtat/amphtml,honeybadgerdontcare/amphtml,lzanol/amphtml,Adtoma/amphtml,jridgewell/amphtml,ecoron/amphtml,Adtoma/amphtml,kixer-com/amphtml,cvializ/amphtml,ecoron/amphtml,aghassemi/amphtml,Gregable/amphtml,dotandads/amphtml,kixer-com/amphtml,avimehta/amphtml,tlong2/amphtml,jpettitt/amphtml,src-code/amphtml,chaveznvg/amphtml,alanorozco/amphtml,burtcorp/amphtml,engtat/amphtml,laterpay/amphtml,DistroScale/amphtml,arealit/amphtml,techhtml/amphtml,gumgum/amphtml,pedjoni8/amphtml,alanorozco/amphtml,camelburrito/amphtml,smartadserver/amphtml,yieldbot/amphtml,danielrozenberg/amphtml,chaveznvg/amphtml,avimehta/amphtml,Adtoma/amphtml,pietergreyling/amphtml,comScore/amphtml,sharethrough/amphtml,DarXector/amphtml,ADITION/amphtml,src-code/amphtml,spotxchange/amphtml,smartadserver/amphtml,sklobovskaya/amphtml,Adtoma/amphtml,fullspeed-sp/amphtml,burtcorp/amphtml,shawnbuso/amphtml,lzanol/amphtml,BenDz/amphtml,ADITION/amphtml,keithwrightbos/amphtml,JuliusThms/amphtml,mhc-gh/amphtml,taboola/amphtml,sebastianbenz/amphtml,clawr/amphtml,gumgum/amphtml,prateekbh/amphtml,DarXector/amphtml,DarXector/amphtml,aghassemi/amphtml,rajkumarsrk/amphtml,adup-tech/amphtml,kamtschatka/amphtml,DAC-f1h-dev/amphtml,wjfang/amphtml,BenDz/amphtml,gumgum/amphtml,nexxtv/amphtml,fullspeed-sp/amphtml,lannka/amphtml,dotandads/amphtml,pedjoni8/amphtml,sklobovskaya/amphtml,powdercloud/amphtml,sortable/amphtml,ampproject/amphtml,lannka/amphtml,cvializ/amphtml,Mobusi-ads/amphtml,engtat/amphtml,yandex-pcode/amphtml,zhucl/amphtml,lannka/amphtml,adup-tech/amphtml,widespace-os/amphtml,Gregable/amphtml,ampproject/amphtml,honeybadgerdontcare/amphtml,DistroScale/amphtml,taboola/amphtml,engtat/amphtml,bpaduch/amphtml,shawnbuso/amphtml,cory-work/amphtml,adup-tech/amphtml,adiant/amphtml,DAC-f1h-dev/amphtml,prateekbh/amphtml,lannka/amphtml,sortable/amphtml,spotxchange/amphtml,lzanol/amphtml,src-code/amphtml,arealit/amphtml,shawnbuso/amphtml,techhtml/amphtml,alanorozco/amphtml,JuliusThms/amphtml,rsimha-amp/amphtml,yieldmo/amphtml,spotxchange/amphtml,media-net/amphtml,donttrustthisbot/amphtml,gumgum/amphtml,widespace-os/amphtml,mhc-gh/amphtml,chaveznvg/amphtml,jdelhommeau/amphtml,laterpay/amphtml,Gregable/amphtml,ampproject/amphtml,kamtschatka/amphtml,camelburrito/amphtml,voyagegroup/amphtml,prateekbh/amphtml,burtcorp/amphtml,cory-work/amphtml,pedjoni8/amphtml,tlong2/amphtml,sriramkrish85/amphtml,zhangsu/amphtml,rsimha-amp/amphtml,sortable/amphtml,sriramkrish85/amphtml,powdercloud/amphtml,zhangsu/amphtml,nexxtv/amphtml,pedjoni8/amphtml,adiant/amphtml,zhangsu/amphtml,taboola/amphtml,erwinmombay/amphtml,kixer-com/amphtml,arealit/amphtml,sriramkrish85/amphtml,mhc-gh/amphtml,jmadler/amphtml,lzanol/amphtml,tlong2/amphtml,taboola/amphtml,DAC-f1h-dev/amphtml,sebastianbenz/amphtml,JuliusThms/amphtml,jridgewell/amphtml,luciancrasovan/amphtml,chaveznvg/amphtml,jmadler/amphtml,shawnbuso/amphtml,sebastianbenz/amphtml,shawnbuso/amphtml,rlugojr/amphtml,BenDz/amphtml,koshka/amphtml,ecoron/amphtml,rajkumarsrk/amphtml,sklobovskaya/amphtml,aghassemi/amphtml,shawnbuso/amphtml,techhtml/amphtml,arealit/amphtml,bpaduch/amphtml,jpettitt/amphtml,keithwrightbos/amphtml,kamtschatka/amphtml,avimehta/amphtml,DistroScale/amphtml,jmadler/amphtml,zhouyx/amphtml,danielrozenberg/amphtml,keithwrightbos/amphtml,donttrustthisbot/amphtml,luciancrasovan/amphtml,sortable/amphtml,dotandads/amphtml,gumgum/amphtml,yandex-pcode/amphtml,pietergreyling/amphtml,voyagegroup/amphtml