Document `extra_templates`
Document `extra_templates`

Fixes #609

longjl/mkdocs,samuelcolvin/mkdocs,michaelmcandrew/mkdocs,ramramps/mkdocs,kubikusrubikus/mkdocs,davidgillies/mkdocs,d0ugal/mkdocs,justinkinney/mkdocs,kubikusrubikus/mkdocs,kubikusrubikus/mkdocs,gregelin/mkdocs,davidgillies/mkdocs,ramramps/mkdocs,mlzummo/mkdocs,nicoddemus/mkdocs,michaelmcandrew/mkdocs,ramramps/mkdocs,jimporter/mkdocs,williamjmorenor/mkdocs,williamjmorenor/mkdocs,vi4m/mkdocs,vi4m/mkdocs,justinkinney/mkdocs,lbenet/mkdocs,fujita-shintaro/mkdocs,jeoygin/mkdocs,jimporter/mkdocs,rickpeters/mkdocs,simonfork/mkdocs,mkdocs/mkdocs,lukfor/mkdocs,mkdocs/mkdocs,cnbin/mkdocs,pjbull/mkdocs,hhg2288/mkdocs,samuelcolvin/mkdocs,mlzummo/mkdocs,tedmiston/mkdocs,dmehra/mkdocs,tedmiston/mkdocs,fujita-shintaro/mkdocs,lukfor/mkdocs,mlzummo/mkdocs,gregelin/mkdocs,cnbin/mkdocs,pjbull/mkdocs,simonfork/mkdocs,waylan/mkdocs,waylan/mkdocs,peter1000/mkdocs,jamesbeebop/mkdocs,pjbull/mkdocs,rickpeters/mkdocs,tedmiston/mkdocs,peter1000/mkdocs,peter1000/mkdocs,jamesbeebop/mkdocs,jeoygin/mkdocs,dmehra/mkdocs,lbenet/mkdocs,d0ugal/mkdocs,justinkinney/mkdocs,samuelcolvin/mkdocs,gregelin/mkdocs,lbenet/mkdocs,jimporter/mkdocs,mkdocs/mkdocs,rickpeters/mkdocs,nicoddemus/mkdocs,vi4m/mkdocs,fujita-shintaro/mkdocs,longjl/mkdocs,michaelmcandrew/mkdocs,simonfork/mkdocs,williamjmorenor/mkdocs,d0ugal/mkdocs,nicoddemus/mkdocs,longjl/mkdocs,hhg2288/mkdocs,hhg2288/mkdocs,jeoygin/mkdocs,cnbin/mkdocs,dmehra/mkdocs,lukfor/mkdocs,jamesbeebop/mkdocs,waylan/mkdocs,davidgillies/mkdocs