[doc] development

@jdiefenbaugh

I broke my conda environment and need to reinstall beat.editor v1 and followed https://gitlab.idiap.ch/beat/beat.editor/blob/master/doc/development.rst

However given that:

$ ../bob.admin/conda/conda-bootstrap.py --overwrite --python=3.6 beatedit

is not valid anymore, can you update the new procedure in the documentation https://gitlab.idiap.ch/beat/beat.editor/blob/master/doc/development.rst ?

Thanks!