Clarify that pip wheels are incompatible with alpine-based images

[smallnamespace]

The current README.md uses the generic language for other images:

This variant is highly recommended when final image size being as small as possible is desired. The main caveat to note is that it does use musl libc instead of glibc and friends, so certain software might run into issues depending on the depth of their libc requirements. However, most software doesn't have an issue with this, so this variant is usually a very safe choice.

However, for Python specifically, manylinux wheels are incompatible with MUSL, so any docker images that end up pulling native dependencies via pip will likely end up having to build from source (see pypa/manylinux#37). For a popular library like pandas, this is the difference between a 1-minute and a 20-minute build time.

This seems like a significant downside to a Python docker image, and probably should be noted in the documentation.

[stefansedich]

+1 we are just spinning up some of our Python services into docker and I have since run into this, I attempted to take the route I used for our minimal Ruby containers but soon ran into issues, for now I have moved to 3.5-slim and will eat the larger images but it would be great to seem some compatible manylinux wheels that work with alpine and better clarification in the docs around the caveats.

[tao12345666333]

In addition, if you pay attention to performance, please check this page http://moelove.info/docker-python-perf/ to see the performance results.

The code is here https://github.com/tao12345666333/docker-python-perf. And the pipeline run every week.

[andelf]

echo "manylinux1_compatible = True" > $PYTHON_PATH/_manylinux.py