Update README.md

#3223 fixed explanation on the main page.
Update README.md
Update README.md
Update README.md

#3222 added warning
Update README.md
Merge branch 'develop'
Releasing version 3.6.5
Update DEVELOPER.md

minor changes to the process of making a new release
Merge pull request #222 from eishub/master_release

Releasing version 3.6.5
Updated working version number to 3.6.6-SNAPSHOT