Markup tips for Markdown shown while editing wiki pages in other formats

Description

We support creating wiki in RDoc / Asciidoc / Org formats, but there a few issues which prevent the process from being as smooth as creating wiki in Markdown:

• In the wiki editor we say:

  To link to a (new) page, simply type [Link Title](page-slug)

This syntax does not work for RDoc (see gitlab-ce#18287). A working syntax for RDoc is here[link:additional-page] (http://stackoverflow.com/questions/2230954/is-there-any-way-to-easily-link-a-file-in-rdoc)

Proposal

Display correct hint how to create a link when non-Markdown formats are selected in the dropdown.