mention REPO and BRANCH in the development documentation

dev/containers/f29-rpms-py3

@@ -18,7 +18,6 @@ RUN dnf -y install \
     which \
     git
 
-# FIXME: this should use $REPO and $BRANCH:
 RUN cd / \
     && git clone -b $BRANCH $REPO \
     && chmod +x /pagure/dev/containers/runtests_py3.sh

doc/development.rst

@@ -317,6 +317,7 @@ Use the following command to run the tests ::
 
 This command will build a fedora based container and execute the test suite. You can also
 limit the tests to unit-test files or single tests similar to the ``python runtests.py``
-options described above.
+options described above. You need set the environment variables REPO and BRANCH if the
+tests are not yet available in the upstream pagure master branch.