Capture style tips and conventions as GitHub issues

This first style guide issue is rather meta. It is a style guide entry about how to build our style guide over time.

Whenever you are dealing with matters of style and convention in Java, Git, GitHub, Slack and the other tools we use together to build Bisq, consider capturing them here in this repository as a GitHub issue. Doing so has a few benefits:

1. It provides a natural place for a conversation to ensue about that style guide entry, and for a rough consensus to form about it.

2. It provides an easily linkable resource for future use, so that style tips don't need to be repeated everywhere. If you're reviewing someone else's work, or refactoring something, you can simply use a GitHub issue reference to the style guide entry in question, e.g. this one, which is bisq-network/style#1.

When a style guide issue has been around for a while and has rough consensus, it can graduate to a written entry in the `README.adoc` file in the root of this repository, and the issue can be closed.

Start by reading this issue and the README.adoc file named in it. Identify a specific style or convention that needs discussion, then use a GitHub issue to document it and build rough consensus; the work is done when an agreed entry can be added to README.adoc.

Written by the indexing model from the issue text.