Mention coala docs url
Mention coala docs url

Closes #201
rhemon/documentation,coala/documentation,Akki356/documentation,kshitijkg01/documentation,Kevchen/documentation,Asnelchristian/documentation,virresh/documentation,coala/documentation,Warewolf96/documentation,AnishHota/documentation,abhishekbundela/documentation,lusy/coala-documentation,coala/documentation,cristinabuciu/documentation