fix(docs/howto-contribute): main repository has moved

docs/howto-contribute.md

@@ -7,20 +7,17 @@ for a good introduction.
 Here are some tips and tricks
 to make the process of contributing as smooth as possible.
 
-1. Use Zulip: https://leanprover.zulipchat.com/#
+1. Use Zulip: https://leanprover.zulipchat.com/
    Discuss your contribution while you are working on it.
 2. Adhere to the guidelines:
    - The [style guide](/docs/style.md) for contributors.
    - The explanation of [naming conventions](/docs/naming.md).
    - The [git commit conventions](https://github.com/leanprover/lean/blob/master/doc/commit_convention.md).
 3. Create a pull request from a feature branch on your personal fork,
-   as explained in the link above.
+   as explained in the link above, or from a branch of the main repository if you have commit access (you can ask for access on Zulip).
 
 
-## The community fork and the nursery
-
-The community also uses https://github.com/leanprover-community/mathlib
-for collaborative contributions: ask on Zulip if you'd like commit access.
+## The nursery
 
 Finally, https://github.com/leanprover-community/mathlib-nursery
 makes it possible to have early access to work in progress.