Add a contrib Dockerfile for local build image on Linux

contrib/Dockerfile

@@ -0,0 +1,15 @@
+FROM readthedocs/build:latest
+
+ARG username
+ARG uid=$uid
+ARG gid=$uid
+
+ENV UID ${uid}
+ENV GID ${gid}
+
+USER root
+RUN groupadd --gid ${GID} docscustom
+RUN usermod --uid ${UID} --gid ${GID} docs
+USER docs
+
+CMD ["/bin/bash"]

contrib/docker_build.sh

@@ -0,0 +1,11 @@
+#!/bin/sh
+
+username=`id -nu`
+uid=`id -u`
+gid=`id -g`
+
+docker build \
+    -t readthedocs/build:latest-dev \
+    --build-arg uid=${uid} \
+    --build-arg gid=${gid} \
+    .

contrib/readme.rst

@@ -1,5 +1,17 @@
+Contrib
+=======
+
+Building development Docker image
+---------------------------------
+
+If you run Linux, you likely need to build a local Docker image that extends our
+default image::
+
+    cd contrib/
+    ./docker_build.sh
+
 Running Read the Docs via Supervisord
-=====================================
+-------------------------------------
 
 This is the easiest way to start all of the commands you'll need for development
 in an environment relatively close to the production evironment. All you need is

docs/development/buildenvironments.rst

@@ -82,3 +82,19 @@ DOCKER_VERSION
     Version of the API to use for the Docker API client.
 
     Default: :djangosetting:`DOCKER_VERSION`
+
+
+Local development
+-----------------
+
+On Linux development environments, it's likely that your UID and GID do not
+match the ``docs`` user that is set up as the default user for builds. In this
+case, it's necessary to make a new image that overrides this user::
+
+    cd contrib/
+    ./docker_build.sh
+
+This will create a new image, ``readthedocs/build:latest-dev``,
+which you can re-tag as ``latest`` to make Read the Docs use this image instead::
+
+  docker tag readthedocs/build:latest-dev readthedocs/build:latest