Instructions to test-drive unreleased code

#42 
Use backpacks around inline code & file names: `Podfile`, `Gemfile`

_PS : I also usually add an empty line after titles lines (`#### xxx`) because some markdown parsers expect one to format it correctly (GitHub is fine without it, but I believe `Mou.app` isn't for example). Not a big deal, but it doesn't hurt :wink:_