Important: Getting Involved pages needs to be rewritten or at least updated

https://matrix.org/docs/guides/getting-involved is probably the first thing many people will click on since it is linked to by that "Learn More" button on the homepage. A ton of the comments I have seen about Matrix 1.0 are asking "Wth is Matrix?".

> Matrix is an ecosystem consisting of several apps written by lots of people.

That page probably needs to be rewritten to explain better what Matrix is.

At a minimum it needs to be updated with current info, it still says things like

> We are still working on the server-server spec

Start with the Getting Involved page at https://matrix.org/docs/guides/getting-involved and review its current wording and outdated Matrix references. Define the information newcomers need about Matrix and update the page so its explanation and project status are current; done means the page clearly answers what Matrix is and how people can get involved.

Written by the indexing model from the issue text.