Fix README installation instructions

[tekktrik]

Library name used underscore instead of hyphen

[FoamyGuy]

it's listed in setup.py with an underscore:

Adafruit_CircuitPython_Bitmap_Font/setup.py

Line 25 in d2dd7db

name="adafruit-circuitpython-bitmap_font",

and pip3 install adafruit-circuitpython-bitmap_font seems to work for installing from pip.

Is there a reason the hyphen is preferred?

[tekktrik]

Oh weird, no, to be completely honest I only ran into while digging into another issue. It really stemmed from how PyPI says to install it:

But if it works otherwise then nevermind!

[FoamyGuy]

Interesting, never noticed that before. It installs correctly with the hyphenated name too. So it seems pip or PyPi silently converts between the two.

I found some related discussion here: ros/rosdistro#18116 which points to a PEP that mentions using underscores is "discouraged": https://www.python.org/dev/peps/pep-0008/#package-and-module-names

It's unclear why it's discouraged but it might be good in the long run for us to move anything that does use underscores to hyphens. If we do that we'll need to make sure there are no adverse consequences for the CI task that publishes to PyPi (i.e. make sure changing the name in setup.py won't freak it out or create a duplicate listing or anything).