contrib/doc/README.ldap-migration should be merged to README.md

Descriptive title for this enhancement

the content of contrib/doc/README.ldap-migration should be merged to README.md

Actual behavior

README.ldap-migration just contains some basic instructions how to migrate actual ldap to FusionDirectory, but thats the only content of the file.

Expected behavior

Have this info onto the README.md

Benefits

More info into REAME.md, easier to find for new users

Possible Drawbacks

none