Added beginner-friendly introduction to Behavior Graphs

[HussainAther]

• Added an easy-to-understand introduction to Behavior Graphs in intro-behavior-graphs.md.
• Explains concepts using simple analogies and examples.
• Aims to help beginners understand how Behavior Graphs work in Hubs.

[DougReeder]

LGTM

[Exairnous]

Thank you for the PR, improving the beginner experience is good to do.

However there are a couple of things.

1. This PR has two very different parts. It adds contribution guidelines to the Hubs Docs repository, and it adds an introduction to Behavior Graphs. While we haven't yet defined a lot of policies around pull requests yet, I would prefer the contribution guidelines be split off into a separate PR.
2. While I do like that your introduction is very beginner friendly and clearly tells people why they would want to use Behavior Graphs, it also feels like it's fighting a bit with the rest of the document, which is also supposed to be an introduction (e.g. with this PR we would have two sections on how Behavior Graphs work). In addition to that, your "Final Thoughts" section combines with the original introduction and makes for a very long section compared to the rest of your introduction. Did you intend this? (Also, it strikes me as a bit weird to have a final thoughts section near the beginning of the page)

Getting back to the contribution guidelines, there are already tentative plans around contribution guidelines and a bigger documentation rewrite, so while your proposed guidelines are generally in line with what we want, this isn't necessarily where they should be added.

This is actually a good time for this discussion, though, as contribution guidelines were one of the next things that were going to be tackled anyway. In light of this, I've added an agenda item for contribution guidelines to the Governance Team meeting tonight. You are welcome to join in and attend the meeting, if you are available (you can find the location/time in the Discord event). Although don't worry if you aren't available, because it's highly unlikely that we'll only be discussing them for one meeting.

[HussainAther]

As suggested by @Exairnous, I’ve split out the contribution guidelines and README changes into a separate PR: #219. This PR now focuses solely on the beginner-friendly introduction to Behavior Graphs.

I’ll follow up soon with improvements to better integrate this intro with the existing documentation structure. Thanks again for the thoughtful feedback!

[Exairnous]

@HussainAther Thank you, and you're welcome. I'll look forward to your improvements.