update nightly build config recommendations

README.md

@@ -105,9 +105,9 @@ this end, add a job like this:
 build-iris.dev:
   <<: *template
   variables:
-    STDPP_REV: "iris/stdpp"
-    IRIS_REV: "iris/iris"
-    OPAM_PINS: "coq version 8.10.dev   git+https://gitlab.mpi-sws.org/$STDPP_REV   git+https://gitlab.mpi-sws.org/$IRIS_REV"
+    STDPP_REPO: "iris/stdpp"
+    IRIS_REPO: "iris/iris"
+    OPAM_PINS: "coq version 8.13.dev   git+https://gitlab.mpi-sws.org/$STDPP_REPO#$STDPP_REV   git+https://gitlab.mpi-sws.org/$IRIS_REPO#$IRIS_REV"
   except:
   only:
   - triggers
@@ -121,8 +121,9 @@ REST API or by a schedule.  The pins are set up to install a development version
 of all the dependencies, and the `8.10` branch of Coq.
 
 The `STDPP_REV` and `IRIS_REV` variables can be set via an API request to test
-this repository against different branches or even forks of std++ and Iris (see
-the `build-all` script in the Iris repository.)
+this repository against different branches of std++ or Iris; `STDPP_REPO` and
+`IRIS_REPO` can be set to fetch those branches from forks (see the `build-all`
+script in the Iris repository.)
 
 Now ask an admin to set up a pipeline schedule.  We usually only
 do nightly builds for projects in the iris group; those schedules should be