PEP 387: Update language around discussion venues, part 2 (#4770)

Co-authored-by: Cody Maloney <cmaloney@users.noreply.github.com>

Author: hugovk

peps/pep-0387.rst

@@ -146,8 +146,12 @@ Making Incompatible Changes
 Making an incompatible change is a gradual process performed over
 several releases:
 
-1. :pep:`PEP 1: Start with an idea <1#start-with-an-idea-for-python>` discussion.
-   If the discussion reaches consensus that acceptance is possible a PEP or
+1. Discuss the change.
+   Depending on the degree of incompatibility, this could be on
+   `Discourse <https://discuss.python.org/>`__,
+   the `issue tracker <https://github.com/python/cpython/issues/>`__,
+   or in an appropriate workgroup or SIG.
+   If the discussion reaches consensus a :pep:`PEP <1>` or
    similar document may be written.
    Hopefully users of the affected API will pipe up to comment.