[PATCH 2/2] docs: Mention Postgres for Docker development install

[Russell Currey]

Might as well since it's there, and it gives some clue to anyone trying
to use Docker on non-x86.  I figured it was best to leave this out of
the README since it's incredibly niche.

Signed-off-by: Russell Currey <ruscur at russell.cc>
---
 docs/development/installation.rst | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/docs/development/installation.rst b/docs/development/installation.rst
index 52dc2c3..0ab755f 100644
--- a/docs/development/installation.rst
+++ b/docs/development/installation.rst
@@ -37,6 +37,10 @@ configure Patchwork using Docker:
 
       $ docker-compose build
 
+   To use Postgres instead of MySQL, give the ``-f docker-compose-pg.yml``
+   argument to ``docker-compose``.  This is required on non-x86 architectures
+   as the MySQL Docker images do not have multiarch support.
+
 #. Run ``docker-compose up``:
 
    .. code-block:: shell
-- 
2.21.0