docs: Updating homepage to new model for 26.04

[asanvaq]

ROCKS-2627
A new model is implemented for the Chisel docs homepage based on the template for 26.04. This includes:

• An updated introduction section to mention what the product is, what the product does, what need the product meets and whom the product is useful for.
• A new "In this documentation" section that systematically exposes the documentation’s contents.
• An updated "How this documentation is organized" section that sets expectations for the reader.
• An updated "Project and Community" section with some information added.

[cjdcordeiro]

thanks for the changes, almost there

[cjdcordeiro]

Thank you very much for all the back and forth. It turned out quite well, and I'm leaving a couple of non-blocking comments for us to follow up on ;)

[cjdcordeiro]

I won't block the PR on this, cause it's quite nuanced, but just food for thought: in the line above, Chisel is depicted as a "developer tool". The conotation is different, which doesn't make the use of "Users" wrong here (IMO), but worth noting, just in case you have a different interpretation

[cjdcordeiro]

Thanks for being willing to try this out.

This looks good enough for now. But I'd like to find a better place for it still.

Just continue discussing the following on the side:

• In the rockcraft docs, there's a special "docs contributions" page (https://documentation.ubuntu.com/rockcraft/stable/contribute-to-this-documentation/). Is that part of the template? If we're having one as well for Chisel, isn't that the obvious place to have this reference? TBC