Add warning to docs re: DELETE_OUTPUT_DIRECTORY
Add warning to docs re: DELETE_OUTPUT_DIRECTORY

Summonee/pelican,UdeskDeveloper/pelican,abrahamvarricatt/pelican,koobs/pelican,Polyconseil/pelican,lazycoder-ru/pelican,joetboole/pelican,joetboole/pelican,talha131/pelican,alexras/pelican,51itclub/pelican,gymglish/pelican,catdog2/pelican,11craft/pelican,ingwinlu/pelican,alexras/pelican,goerz/pelican,farseerfc/pelican,jimperio/pelican,51itclub/pelican,douglaskastle/pelican,deved69/pelican-1,Scheirle/pelican,TC01/pelican,florianjacob/pelican,ingwinlu/pelican,zackw/pelican,getpelican/pelican,kennethlyn/pelican,51itclub/pelican,sunzhongwei/pelican,Scheirle/pelican,zackw/pelican,number5/pelican,abrahamvarricatt/pelican,liyonghelpme/myBlog,fbs/pelican,gymglish/pelican,crmackay/pelican,Polyconseil/pelican,arty-name/pelican,janaurka/git-debug-presentiation,UdeskDeveloper/pelican,karlcow/pelican,Summonee/pelican,deved69/pelican-1,simonjj/pelican,kernc/pelican,GiovanniMoretti/pelican,liyonghelpme/myBlog,GiovanniMoretti/pelican,ls2uper/pelican,liyonghelpme/myBlog,sunzhongwei/pelican,HyperGroups/pelican,jo-tham/pelican,liyonghelpme/myBlog,garbas/pelican,abrahamvarricatt/pelican,janaurka/git-debug-presentiation,simonjj/pelican,kernc/pelican,koobs/pelican,catdog2/pelican,rbarraud/pelican,garbas/pelican,kennethlyn/pelican,ehashman/pelican,kennethlyn/pelican,iKevinY/pelican,liyonghelpme/myBlog,lucasplus/pelican,GiovanniMoretti/pelican,rbarraud/pelican,douglaskastle/pelican,ionelmc/pelican,eevee/pelican,lazycoder-ru/pelican,simonjj/pelican,iurisilvio/pelican,jvehent/pelican,jimperio/pelican,catdog2/pelican,btnpushnmunky/pelican,lucasplus/pelican,Scheirle/pelican,levanhien8/pelican,TC01/pelican,deanishe/pelican,Rogdham/pelican,deanishe/pelican,florianjacob/pelican,rbarraud/pelican,11craft/pelican,0xMF/pelican,talha131/pelican,treyhunner/pelican,number5/pelican,ehashman/pelican,avaris/pelican,levanhien8/pelican,ls2uper/pelican,eevee/pelican,eevee/pelican,UdeskDeveloper/pelican,iKevinY/pelican,zackw/pelican,janaurka/git-debug-presentiation,treyhunner/pelican,btnpushnmunky/pelican,HyperGroups/pelican,JeremyMorgan/pelican,goerz/pelican,florianjacob/pelican,lucasplus/pelican,iurisilvio/pelican,gymglish/pelican,btnpushnmunky/pelican,kernc/pelican,jo-tham/pelican,TC01/pelican,avaris/pelican,11craft/pelican,Rogdham/pelican,HyperGroups/pelican,iurisilvio/pelican,ls2uper/pelican,jvehent/pelican,goerz/pelican,crmackay/pelican,deanishe/pelican,number5/pelican,JeremyMorgan/pelican,sunzhongwei/pelican,jimperio/pelican,levanhien8/pelican,karlcow/pelican,jvehent/pelican,alexras/pelican,ehashman/pelican,Rogdham/pelican,garbas/pelican,getpelican/pelican,crmackay/pelican,treyhunner/pelican,joetboole/pelican,JeremyMorgan/pelican,koobs/pelican,deved69/pelican-1,sunzhongwei/pelican,douglaskastle/pelican,Summonee/pelican,karlcow/pelican,justinmayer/pelican,lazycoder-ru/pelican,farseerfc/pelican