edit: add documentation

* Add documentation to plugins/edit.rst about the execution of the
plugin during the importer.

docs/plugins/edit.rst

@@ -23,6 +23,30 @@ The ``edit`` command has these command-line options:
   (in addition to the defaults set in the configuration).
 - ``--all``: Edit *all* available fields.
 
+Interactive Usage
+-----------------
+
+The ``edit`` plugin can also be invoked during an import session. If enabled, it
+adds two new options to the user prompt::
+
+    [A]pply, More candidates, Skip, Use as-is, as Tracks, Group albums, Enter search, enter Id, aBort, eDit, edit Candidates?
+
+- ``eDit``: use this option for using the original items' metadata as the
+  starting point for your edits.
+- ``edit Candidates``: use this option for using a candidate's metadata as the
+  starting point for your edits.
+
+Please note that currently the interactive usage of the plugin will only allow
+you to change the item-level fields. In case you need to edit the album-level
+fields, the recommended approach is to invoke the plugin via the command line
+in album mode (``beet edit -a QUERY``) after the import.
+
+Also, please be aware that the ``edit Candidates`` choice can only be used with
+the matches found during the initial search (and currently not supporting the
+candidates found via the ``Enter search`` or ``enter Id`` choices). You might
+find the ``--search-id SEARCH_ID`` :ref:`import-cmd` option useful for those
+cases where you already have a specific candidate ID that you want to edit.
+
 Configuration
 -------------