Update docs/settings.rst
Update docs/settings.rst

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