fix ciphers link (#8799)

certbot/docs/ciphers.rst

@@ -1,3 +1,11 @@
+..
+  Sphinx complains that this file isn't included in any toctree, however, we
+  currently link to it in the section about installing Certbot through Docker.
+  Setting :orphan: below suppresses this warning. See
+  https://www.sphinx-doc.org/en/master/usage/restructuredtext/field-lists.html#special-metadata-fields.
+
+:orphan:
+
 ============
 Ciphersuites
 ============

certbot/docs/conf.py

@@ -98,7 +98,6 @@ language = None
 exclude_patterns = [
     '_build',
     'challenges.rst',
-    'ciphers.rst'
 ]
 
 # The reST default role (used for this markup: `text`) to use for all