[Learnosm-coord] LearnOSM procedures

[althio]

Nick has done a very good job of documenting the LearnOSM procedures
as part of his document on the filling system.

As discussed previously in the Training WG or recently with Claire, at
one point we will need procedures and a documentation unified
somewhere. Maybe in CONTRIBUTING.md on GitHub?
LearnOSM website and the wiki could simply redirect to this file.


I also found bits of information and references so I will share it
here with a list of links.
I proposed a Pull Request to add some links in CONTRIBUTING.md to
https://github.com/hotosm/learnosm/wiki/* because these things are
documented but quite hidden.


Structure, folders, file names
https://github.com/hotosm/learnosm/wiki/File-naming-in-_posts-directory
https://github.com/hotosm/learnosm/issues/10

Front matter for guide documents
https://github.com/hotosm/learnosm/blob/gh-pages/CONTRIBUTING.md#front-matter-for-guide-documents

Content formatting
https://github.com/hotosm/learnosm/wiki/Markdown-post-guidelines
https://github.com/hotosm/learnosm/issues/15
https://guides.github.com/features/mastering-markdown/

Style guide
https://hackpad.com/Proposed-Style-Guide-for-LearnOSM-1JJxS8NIQSX
https://github.com/hotosm/learnosm/issues/82
https://github.com/hotosm/learnosm/issues/324

Images
https://github.com/hotosm/learnosm/wiki/Images-guidelines-beta
hotosm/learnosm#94
hotosm/learnosm#113
hotosm/learnosm#118
hotosm/learnosm#20
hotosm/learnosm#10 (comment)
hotosm/learnosm#95 (comment)
hotosm/learnosm#306 (comment)