Provide contributing guidelines

[tboeghk]

We should utilize GH issue and pull request template as well as contributing guidelines to make it easier for contributors to add components. The data format is still work in progress, but as soon it is stable, we should get this going.

• Add code of conduct
• Add contributing guidelines
  • Describe the perfect Solr package Github repo
• Add pull request template

[tboeghk]

While iterating through the packages listed it seems there is a lot of grunt work to do :-/

Most packages are hosted on GitHub (which makes things accessible using their API). Some packages publish their releases on Maven Central but do not release their JARs on GitHub. Some other mark releases but do not release JARs anywhere. Some other plugins have issues with their release naming (must match \d+\.\d+\.\d+).

I'll write down a guide how to properly release a Solr package on GitHub (marking a release, uploading JARs) using Maven and issue pull requests to some of the maintained packages.