Improve "What is conda forge" section in introduction.

### Where should the content be added?

A brief introduction / What is conda-forge? / [Becoming involved.](https://conda-forge.org/docs/user/introduction.html)

### What should be added?

The line

`Cannot find a package or only outdated versions of a package? - Everybody is welcome to contribute to our package stack! Please refer to [Becoming involved](https://conda-forge.org/docs/user/contributing.html#becoming-involved), for an overview on how to start contributing.`

Suggests that a person can only get involved around packages. However, the words can be modified to welcome other contributions as well.

Also, maybe there can be a separate paragraph for 'Becoming involved' under 'What is conda-forge' so that it's more prominent.

### Additional information

_No response_