Update Dockerfile to use Python3.6 and install from PyPI package

Also update README and CONTRIBUTING guides with the information
on how to build and run Docker image.

CONTRIBUTING.md

@@ -241,3 +241,21 @@ DRAFT
    I think this is required for PyPI description to look nice.
 7. `python setup.py sdist` to build the package
 8. `twine upload dist/coursera-dl-0.6.1.tar.gz` to deploy the package.
+
+## Docker
+
+Build new Docker image from PyPI package:
+
+```
+docker build --tag courseradl/courseradl --build-arg VERSION=0.11.2 .
+```
+
+Run the image:
+```
+docker run --rm -it -v "$(pwd):/courses" -v "$HOME/.netrc:/netrc" courseradl -n /netrc -- google-machine-learning
+```
+
+Publish the image:
+```
+docker push courseradl/courseradl
+```

Dockerfile

@@ -1,21 +1,14 @@
-FROM python:3.4-slim
+FROM python:3.6-slim
 
-LABEL maintainer "opsxcq@strm.sh"
-
-WORKDIR /src
-COPY requirements.txt /src
-
-COPY requirements-dev.txt /src
+LABEL maintainer "https://github.com/coursera-dl/"
 
 RUN apt-get update && \
     apt-get install -y --no-install-recommends gcc g++ libssl-dev && \
     rm -rf /var/lib/apt/lists/* && \
-    pip install -r requirements.txt && \
-    pip install -r requirements-dev.txt && \
     apt-get purge -y --auto-remove gcc g++ libssl-dev
 
-COPY . /src
-RUN python setup.py install
+ARG VERSION
+RUN pip install coursera-dl==$VERSION
 
 WORKDIR /courses
 ENTRYPOINT ["coursera-dl"]

README.md

@@ -220,26 +220,37 @@ applicable).
 If you prefer you can run this software inside Docker:
 
 ```
-docker run --rm -it \
-       -v "$(pwd):/courses" \
-       strm/coursera-dl \
-       -u <USER> -p <PASSWORD>
+docker run --rm -it -v \
+    "$(pwd):/courses" \
+    courseradl/courseradl -u <USER> -p <PASSWORD>
 ```
 
-The actual working dir for coursera-dl is /courses, all courses will be downloaded there if you don't specify otherwise.
+Or using netrc file:
+
+```
+docker run --rm -it \
+    -v "$(pwd):/courses" -v "$HOME/.netrc:/netrc" \
+    courseradl/courseradl -n /netrc
+```
+
+The actual working dir for coursera-dl is /courses, all courses will be
+downloaded there if you don't specify otherwise.
 
 ## Windows
 
 `python -m pip install coursera-dl`
 
-Be sure that the Python install path is added to the PATH system environment variables. This can be found in Control Panel > System > Advanced System Settings > Environment Variables. 
+Be sure that the Python install path is added to the PATH system environment
+variables. This can be found in Control Panel > System > Advanced System
+Settings > Environment Variables. 
 
 ```
 Example:
 C:\Python35\Scripts\;C:\Python35\;
 ```
 
-Or if you have restricted installation permissions and you've installed Python under AppData, add this to your PATH.
+Or if you have restricted installation permissions and you've installed Python
+under AppData, add this to your PATH.
 
 ```
 Example: