Add build instructions to readme.
Add build instructions to readme.

I really only do this as a full section because I like to have a scornful one-word section, and sideeye anyone who does have more than a single word in their building instructions.

Signed-off-by: Eric Myhre <2346ad27d7568ba9896f1b7da6b5991251debdf2@exultant.us>

polydawn/gosh,polydawn/gosh