fix links

README.rst

@@ -79,7 +79,7 @@ then
 
 ``tox``
 
-It's also possible to create a ``./secrets.json`` as above, and [build the docker image](#building-a-docker-image). Then::
+It's also possible to create a ``./secrets.json`` as above, and `build the docker image`_. Then::
 
     # For some reason, tox runs faster in an interactive shell and hangs without
     docker run -i scriptworker-test-$PY_DOT_VERSION bash -il  # interactive shell
@@ -89,8 +89,10 @@ It's also possible to create a ``./secrets.json`` as above, and [build the docke
 GPG Homedir testing
 ^^^^^^^^^^^^^^^^^^^
 
-Sometimes it's nice to be able to test things like ``rebuild_gpg_homedirs``.  To do so, [build the docker image](#building-a-docker-image), then::
+Sometimes it's nice to be able to test things like ``rebuild_gpg_homedirs``.  To do so, `build the docker image`_, then::
 
     docker run -i scriptworker-test bash -il
     # in the docker shell,
     rebuild_gpg_homedirs gnupg.yaml
+
+.. _build the docker image: #building-a-docker-image