Update contributing guide

[fdiblen]

Update contributing guide for both the template repository and the generated package:

• Use markdown file from https://github.com/matchms/matchms/blob/master/CONTRIBUTING.md
• Add other type of contributions
  • Spreading the word (LinkedIn, blog posts, Twitter, Reddit etc.)
• Point to README.dev.md for developer documentation

[egpbos]

The matchms version looks better, good idea to update the template one!

These files are almost the same for template and generated package, so to clean up issues, I'm merging this with #157.