Add information on adding in soundtrack/music (#42)

Please let me know if the Steam Community link is not the most optimal source.

readme.md

@@ -94,3 +94,18 @@ next to that and copy `pak0.pak` there, e.g.:
 * Ubuntu: `Quake\id1\pak0.pak`
 
 Then vkQuake is ready to play.
+
+# Optional - Music / Soundtrack
+
+The original quake had a great soundtrack by Nine Inch Nails. Unfortunately, the Steam version does not come with the soundtrack files. The GOG-provided files need to be before they are ready for use. In general, you'll just need to move a "music" folder to the correct location within your vkQuake installation (.e.g `/usr/share/quake/id1/music`). Most Quake engines play nicest with soundtracks placed in the `id1/music` subfolder vs. `sound\cdtracks`
+
+QuakeSpasm, the engine vkQuake is derived from, supports OGG, MP3, and WAV audio formats. The Linux version of QuakeSpasm/VkQuake requires external libraries: libogg or libvorbis for OGG support, and libmad or libmpg123 for MP3. If you already have a setup that works for the engine you're currently using, then you don't necessarily have to change it. 
+
+Generally, the below setup works for multiple engines, including Quakespasm/vkQuake:
+
+* The music files are loose files, NOT inside a pak or pk3 archive.
+* The files are placed inside a "music" subfolder of the "id1" folder. For missionpack or mod soundtracks, the files are placed in a "music" subfolder of the appropriate game folder. So the original Quake soundtrack files go inside "id1\music", Mission Pack 1 soundtrack files go inside "hipnotic\music", and Mission Pack 2 soundtrack files go inside "rogue\music".
+* The files are named in the pattern "tracknn", where "nn" is the CD track number that the file was ripped from. Since the soundtrack starts at the second CD track, MP3 soundtrack files are named "track02.mp3", "track03.mp3", etc. OGG soundtrack files are named "track02.ogg", "track03.ogg", etc.
+
+**See more:** [Quake Soundtrack Solutions (Steam Community)](http://steamcommunity.com/sharedfiles/filedetails/?id=119489135)
+