Say what OpenBot is, and point at the page about it (#7)

The README opened on what a Bot gets without ever saying what the thing is:
a platform that runs in your own infrastructure, with your database, your
model credential and three teammates that are configuration rather than code.
It also never explained that a Bot is any AG-UI endpoint, which is the reason
it works with agents nobody here wrote.

Links copilotkit.ai/openbot from the header and the documentation list.