AVRO-3623: Update the PR template

[RyanSkraba]

I picked the Apache Flink style to illustrate -- I like the way that most of the instructions are in the comments and only the essential text is required for the reviewer.

The original: https://github.com/apache/flink/blob/master/.github/PULL_REQUEST_TEMPLATE.md

Jira

• My PR addresses the following Avro Jira issues and references them in the PR title. For example, "AVRO-1234: My Avro PR"
  • https://issues.apache.org/jira/browse/AVRO-3623
  • In case you are adding a dependency, check if the license complies with the ASF 3rd Party License Policy.

Tests

• does not need testing for this extremely good reason: Non-code change

Commits

• My commits all reference Jira issues in their subject lines. In addition, my commits follow the guidelines from "How to write a good git commit message":
  1. Subject is separated from body by a blank line
  2. Subject is limited to 50 characters (not including Jira issue reference)
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"

Documentation

• In case of new functionality, my PR adds documentation that describes how to use it.
  • All the public functions and the classes in the PR contain Javadoc that explain what it does

[iemejia]

Nice! It looks muuuch better than the one before, let a comment to try to make the process simpler.

[RyanSkraba]

Is there a generic way to say "Javadoc" that includes in-line code documentation like doxygen and python docs?