Update documentation and tips for projectile keys
Merge pull request #646 from hron/update-documentation-for-projectile-keys

Update documentation and tips for projectile keys
Added M-X to README [Close #621]
Merge pull request #649 from k1-hedayati/update-readme-for-smex-major-mode-binding

Added M-X to README
Merge remote-tracking branch 'bbatsov/master' into bbatsov-master