How to turn a package into something pip can install

[Roy Smith]

I want to use (https://github.com/timetric/python-metar).  Our 
deployment process more or less requires that it be installed via pip.  
We maintain our own cache of packages and install using:

pip install --no-index --quiet --find-links packages --requirement 
requirements.txt 

What I can't figure out is what I need to do to go from a clone of the 
github repo to a tarball I can drop into our packages directory.  Is 
there some tutorial somewhere that explains this?