draw a clear line between installing bob packages for using only and installing with buildout for development.

We have to draw a clear line between installing bob packages for using only and installing with buildout for development. Now that we are advertising people to use conda and pip for installation, we need to reflect that in our documentation too. For example, all the commands in the documentations start with ./bin/ which is not really necessary and confusing to people not using buildout. Example: https://www.idiap.ch/software/bob/docs/latest/bioidiap/bob.db.voxforge/master/index.html#getting-the-data