Centralize documentation for developers

[jonwzheng]

Motivation

In #2703, we are moving information from the (difficult-to-maintain, outdated, and generally out-of-the-way) Wiki page to the main documentation + other parts of Github that receive more visibility.

This includes:

• The RMG docs at https://reactionmechanismgenerator.github.io/RMG-Py/ (see [Docs] Update docs website with GitHub wiki info #2707)
• A new CONTRIBUTING.md file (see [Docs] Add CONTRIBUTING file with contributor guidelines #2705)

Issue

However, there isn't really a home for dev-specific information. Specifically, information like:

• how to package a new release (outdated)
• how to update both RMG-Py/RMG-database (outdated)
• ...or anything else useful just to the dev team - such as the latest on how to work w/ Julia

Solution

Ideally we have something that's just out of the way from the users so they don't get confused, but also not tucked away so much that it gets forgotten. And there's always the mental load of having to think of yet another platform for information.

We could even actually just use the Wiki but keep it to just like 1-3 pages so it's more manageable.

I welcome anyone's thoughts on this!