FreqTrace v0.5.0

Signed with an Apple Development certificate (not notarized). Opens cleanly on Macs that trust this developer; generally blocked on others.
On an unrecognized Mac, first launch: right-click FreqTrace.app > Open > Open.

What's Changed

• Add user-facing install & run docs to README by @vk0eppel in #61

Full Changelog: v0.4.2...v0.5.0