[5.1.x] Added some heading labels to to docs/topics/cache.txt.

Backport of 6d1cf53 from main

docs/topics/cache.txt

@@ -256,6 +256,8 @@ Unlike other cache backends, the database cache does not support automatic
 culling of expired entries at the database level. Instead, expired cache
 entries are culled each time ``add()``, ``set()``, or ``touch()`` is called.
 
+.. _database-caching-creating-the-table:
+
 Creating the cache table
 ~~~~~~~~~~~~~~~~~~~~~~~~
 
@@ -282,6 +284,8 @@ table. It will only create missing tables.
 To print the SQL that would be run, rather than run it, use the
 :option:`createcachetable --dry-run` option.
 
+.. _database-caching-multiple-databases:
+
 Multiple databases
 ~~~~~~~~~~~~~~~~~~
 
@@ -324,6 +328,8 @@ the cache backend will use the ``default`` database.
 And if you don't use the database cache backend, you don't need to worry about
 providing routing instructions for the database cache model.
 
+.. _filesystem-caching:
+
 Filesystem caching
 ------------------
 
@@ -411,6 +417,8 @@ cross-process caching is possible. This also means the local memory cache isn't
 particularly memory-efficient, so it's probably not a good choice for
 production environments. It's nice for development.
 
+.. _dummy-caching:
+
 Dummy caching (for development)
 -------------------------------
 
@@ -428,6 +436,8 @@ activate dummy caching, set :setting:`BACKEND <CACHES-BACKEND>` like so::
         }
     }
 
+.. _using-a-custom-cache-backend:
+
 Using a custom cache backend
 ----------------------------