gitlab-shell: use make build instead of bin/compile

What does this MR do?

Update the install-from-source docs so we use make build instead of bin/compile. This is important for a future where we remove the bin/compile script.

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• Documentation created/updated or follow-up review issue created
• Style guides
• Separation of EE specific content

Part of gitlab-shell#173 (closed)