Bring all Dockerfiles for supported Python runtimes into FDK repo (#76)

* Bring all supported Python runtimes to FDK repo

* fixing README

Author: denismakogon

images/README.md

@@ -3,12 +3,22 @@ Image on Docker Hub: https://hub.docker.com/r/fnproject/python
 ## Building Python images
 
 ```sh
-pushd build/3.7.1; docker build -t fnproject/python:3.7.1-dev .; popd
+pushd build-stage/3.6; docker build -t fnproject/python:3.6-dev .; popd
+pushd runtime/3.6; docker build -t fnproject/python:3.6 .; popd
+```
+
+```sh
+pushd build-stage/3.7.1; docker build -t fnproject/python:3.7.1-dev .; popd
 pushd runtime/3.7.1; docker build -t fnproject/python:3.7.1 .; popd
 ```
 
 Then push:
 
+```sh
+docker push fnproject/python:3.6-dev
+docker push fnproject/python:3.6
+```
+
 ```sh
 docker push fnproject/python:3.7.1-dev
 docker push fnproject/python:3.7.1

images/build-stage/3.6/Dockerfile

@@ -0,0 +1,3 @@
+FROM python:3.6-slim-stretch
+
+RUN apt-get update && apt-get install --no-install-recommends -qy build-essential gcc && apt-get clean

images/build-stage/3.7.1/Dockerfile

@@ -0,0 +1,3 @@
+FROM python:3.7.1-slim-stretch
+
+RUN apt-get update && apt-get install --no-install-recommends -qy build-essential gcc && apt-get clean

images/runtime/3.6/Dockerfile

@@ -0,0 +1 @@
+FROM python:3.6-slim-stretch