update links to branches for older Coq versions

README.md

@@ -33,9 +33,7 @@ This version is known to compile with:
  - Coq 8.11.2 / 8.12.2 / 8.13.1
  - A development version of [std++](https://gitlab.mpi-sws.org/iris/stdpp)
 
-If you need to work with Coq 8.7 or Coq 8.8, please check out the
-[iris-3.2 branch](https://gitlab.mpi-sws.org/iris/iris/tree/iris-3.2).
-For Coq 8.9, you can use the
+If you need to work with Coq 8.9 or Coq 8.10, you can use the
 [iris-3.3 branch](https://gitlab.mpi-sws.org/iris/iris/tree/iris-3.3).
 
 ### Working *with* Iris