Update INSTALL.md

[Timdebruijn]

libpq-dev is needed for installing psycopg2 with pip. Without installing libpq-dev this would be the result:

" Command "python setup.py egg_info" failed with error code 1 in /tmp/pip-install-f6iz22g_/psycopg2/ "

"pg_config is required to build psycopg2 from source."

[realsdx]

I think changing the requirement of psycopg2 to psycopg2-binary will solve the issue.

[paseaf]

had the same issue. Good to see there is already a PR

[johnnykv]

thanks!