[doc] no inline html in markdown

[datanel]

• replaced <br> by \ https://github.github.com/gfm/#example-658

[pbougue]

It's OK to merge that for me (:tada: editorconfig for all).

Although, I vote against the 2-trailing-spaces (but if the majority is in favor, let's go for it!).

My arguments are:
"meaningful invisible characters" are not natural and it's easy to mistakenly remove those.
\s\s\n means newline, but not \n alone or \s\s alone.
<br> works for md on github, gitlab and when using those md through slate (see doc.navitia.io).

To me this surpasses respecting strict md and removing any useless html in it.

[woshilapin]

I'm neither for <br> nor \s\s\n, I would just remove these 2 options from our Markdown toolbox. But that's just my opinion. I'll let you decide what's best.

[pbougue]

The .editorconfig was fine for me, removing all trailing even in md files (but maybe one more tool...).
🎉 for \ 😄