Update README
Update README

Identify the recommended development compiler.
Add a section about clippy.
Include a section about the D-Bus based tests.

Signed-off-by: mulhern <7b51bcf507bcd7afb72bf8663752c0ddbeb517f6@redhat.com>

stratis-storage/stratisd,stratis-storage/stratisd,stratis-storage/stratisd,trgill/stratisd,trgill/stratisd