Add first draft of @def-lkb's post

This guest post covers both ocp-indent and merlin
Spelling etc.
Reword according to @Chris00's suggestion.
Rewording.
Add merlin screenshot
Edits to merlin post; add multiple authors experimentally
Merge pull request #14 from ocaml/merlin

Add first draft of @def-lkb's post (for 20 Aug?)