index.rst: Add hint to use --json and --format
index.rst: Add hint to use --json and --format

Added small description for --json and --format
when used with coala command.

Closes https://github.com/coala/documentation/issues/278

coala/documentation,coala/documentation,kshitijkg01/documentation,Warewolf96/documentation,Asnelchristian/documentation,rhemon/documentation,AnishHota/documentation,coala/documentation