Add a note to Debian regarding locales included by default and especially how to make others available

debian/content.md

@@ -17,6 +17,18 @@ The mirror of choice for these images is [the httpredir.debian.org redirecting m
 
 If you find yourself needing a Debian release which is EOL (and thus only available from [archive.debian.org](http://archive.debian.org)), you should check out [the `debian/eol` image](https://hub.docker.com/r/debian/eol/), which includes tags for Debian releases as far back as Potato (Debian 2.2), the first release to fully utilize APT.
 
+## Locales
+
+Given that it is a faithful "minbase" install of Debian, this image only includes the `C`, `C.UTF-8`, and `POSIX` locales by default. For most uses requiring a UTF-8 locale, `C.UTF-8` is likely sufficient (`-e LANG=C.UTF-8` or `ENV LANG C.UTF-8`).
+
+For uses where that is not sufficient, other locales can be installed/generated via the `locales` package. [PostgreSQL has a good example of doing so](https://github.com/docker-library/postgres/blob/69bc540ecfffecce72d49fa7e4a46680350037f9/9.6/Dockerfile#L21-L24), copied below:
+
+```dockerfile
+RUN apt-get update && apt-get install -y locales && rm -rf /var/lib/apt/lists/* \
+	&& localedef -i en_US -c -f UTF-8 -A /usr/share/locale/locale.alias en_US.UTF-8
+ENV LANG en_US.utf8
+```
+
 ## How It's Made
 
 If you are curious about what goes into creating this image, please see [`contrib/mkimage.sh` in `github.com/docker/docker`](https://github.com/docker/docker/blob/master/contrib/mkimage.sh) (and [`contrib/mkimage/debootstrap` in the same repo](https://github.com/docker/docker/blob/master/contrib/mkimage/debootstrap)).