install libGL if it's not already installed

[RSDK-10249] try to ensure that libGL is installed (#36)

The issue Rand had run into was that her Raspian Lite installation didn't include libGL.so.1, so the module couldn't load its libraries properly. 

I spent the morning fighting with PyInstaller to try to convince it to include that file in the binary it creates, and eventually gave up and wrote a first_run.sh instead.

I've tried out the first_run.sh script locally: it appears to work on Ubuntu. I've also ensured that `make dist/archive.tar.gz` packages everything up correctly. I haven't tried it in more detail, though.


* try to ensure that libGL is installed

* add note to readme

* also run apt-get update first