Remove duplication of cordova-docs content from other places

Some content of the cordova-docs docs (README) are duplicated at other locations, which has the danger of these duplications to go out of date.

https://github.com/apache/cordova-coho/blob/10ea350f96e76a54f449578878de48b924778601/docs/plugins-release-process.md#post-blog-post contains parts of the build process.