Rename to PEP-776 and add discussion link

Author: hoodmane

peps/pep-TBD.rst peps/PEP-776.rstpeps/pep-TBD.rst renamed to peps/PEP-776.rst

@@ -1,6 +1,6 @@
 Author: Hood Chatham <roberthoodchatham at gmail.com>
 Sponsor: Łukasz Langa <lukasz at python.org>, Russell Keith-Magee <russell at keith-magee.com>
-Discussions-To:
+Discussions-To: https://discuss.python.org/t/pep-776-emscripten-support/84996
 Status: Draft
 Type: Standards Track
 Topic: Packaging