v21.3.0
doc/start: Improve beginners-guide.rst
doc/start/ceph.conf: trim the sample ceph.conf file
doc/start: Clarify doc building and begin list of conventions
doc/start: Update and fix get-involved.rst
docs/start: Reflect multi-arch support for SMB service
doc/start: Mention RGW in Intro to Ceph
doc/start/os-recommendations: update for Umbrella and future releases
doc: remove references to ceph-deploy