Add context to WPORG readme

[jeffpaul]

The readme.txt currently has extremely minimal context for display on the WPORG plugin page.

Let's look to give a bit more context on the features available and upcoming roadmap items for the non-technical users.

Then let's look to add another section that highlights items of note for developers to show them what to check out if they want to extend the plugin, build their own experiments, or extract out functionality for their own uses (nudging them along the way to consider contributing back to the GitHub repo). Will also want to call out the Abilities Explorer, MCP demo, and any other Developer Experience items that are worth calling out.

Finally, we'll want to look at aligning much of this into the readme.md file while noting the audience coming to GitHub is likely more technical and thus doesn't need to be an exact match to the WPORG readme.txt file contents.