Highlight important facts (fsid and monitor key)

Update the README with an entry for the fsid and monitor keys. We
dediced to remove every key from the default variables.

Signed-off-by: Sébastien Han <sebastien.han@enovance.com>
Merge pull request #57 from leseb/fix-readme

Highlight important facts (fsid and monitor key)
Fix README typo

Fix typo