DOCS: IMDG Reference Manual: Minor improvement propositions for intro page - Contributing chapter

https://github.com/hazelcast/imdg-docs/blob/master/docs/modules/ROOT/pages/index.adoc

1. Developing with Git: Document that explains -> As for me, link name (as well as Confluence page) is a bit confusing - I’m expecting some description of GIT, not HZ, when looking at “Development with GIT”, let me propose to rename it to “Hazelcast Git workflow”
2. explains the branch mechanism of Hazelcast -> it sounds like HZ haz it’s own branching mechanism. In fact, we are using some workflow. I would recommend to use common terms “Branching workflow” or “branching strategy”
3. Hazelcast and how to request changes - > I think “changes” is not fully correct here. Link describes full GIT development cycle, hence, it would be better to use something like “and how to contribute to HZ ”
4. You can contribute to the Hazelcast IMDG code, report a bug, or request an enhancement ->Not sure, but it seems, it would be better to put some encourage in the text, not just highlight technical fact. See, for example, Cassandra page - https://cassandra.apache.org/doc/latest/development/gettingstarted.html. Probably, something like “You are welcomed to contribute to HZ in following ways: ” would be more appreciated by readers