New how-to page covering community module browsing, custom sources (any
Git host, local paths), discovery vs direct mode, local development
workflow, and the --custom-source CLI flag. Clarifies that
.claude-plugin/ is a cross-tool convention, not Claude-specific.
Also updates non-interactive installation docs with the new flag and
examples, bumps sidebar ordering, and fixes --custom-source to install
only core + custom modules when --modules is not specified.
Brian Madison