Nannou: alsa dependency

[freesig]

nannou just failed to build on my ubuntu because of a the cpal dependency on ALSA.
It's actually because I didn't have pkg-config installed although with it installed it still can't find alsa.
We should list these types of dependencies on in the readme for future users.

[freesig]

Ok so to get nannou / cpal to work on my ubuntu I needed:
pkg-config
libasound2-dev

[mitchmindtree]

I think it might just be libasound2-dev that is needed? I think that's all travis needs looking at the .travis.yml, but maybe it comes with pkg-config on linux out of the box or something

[freesig]

Yeh I think it's this line
https://github.com/tomaka/cpal/blob/c2d606176a88ae9610e2b7f17b844f04eccd320e/alsa-sys/build.rs#L4
We could even change this from unrwap to a healpful
.expect("Could not find alsa on your machine.\n Please make sure you have pkg-config and libasound2-dev");