docs(workflow-sharing): add list --shared arguments (reanahub#190)

Adds extra docs for `list` command to the docs for new sharing related
arguments.

Closes reanahub/reana-client#687

docs/reference/reana-client-cli-api/index.md

@@ -126,7 +126,20 @@ List all workflows and sessions.
 The ``list`` command lists workflows and sessions. By default, the list of
 workflows is returned. If you would like to see the list of your open
 interactive sessions, you need to pass the ``--sessions`` command-line
-option.
+option. If you would like to see the list of all workflows, including those
+shared with you, you need to pass the ``--shared`` command-line option.
+
+Along with specific user emails, you can pass the following special values 
+to the ``--shared-by`` and ``--shared-with`` command-line options:
+
+  - ``--shared-by anybody``: list workflows shared with you by anybody.
+
+  - ``--shared-with anybody``: list your shared workflows exclusively.
+
+  - ``--shared-with nobody``: list your unshared workflows exclusively.
+
+  - ``--shared-with [email protected],[email protected]``: list workflows shared
+  with either [email protected] or [email protected]
 
 Example:
 
@@ -136,6 +149,12 @@ Example:
 
   $ reana-client list --verbose --bytes
 
+  $ reana-client list --shared
+
+  $ reana-client list --shared-by [email protected]
+
+  $ reana-client list --shared-with anybody
+
 ### create
 
 Create a new workflow.