Updates for 2025-Apr-01 (#677)

* Move optional steps for testing VMs out of README.md file
This may help avoid new users being confused that they must follow
those instructions.

Signed-off-by: Andy Fingerhut <andy_fingerhut@alum.wustl.edu>

* Add 2025-Jan-30 versions of source code for install.sh

Signed-off-by: Andy Fingerhut <andy_fingerhut@alum.wustl.edu>

* Updates to source code versions for 2025-Apr-01

Signed-off-by: Andy Fingerhut <andy_fingerhut@alum.wustl.edu>

---------

Signed-off-by: Andy Fingerhut <andy_fingerhut@alum.wustl.edu>

Author: jafingerhut

vm-ubuntu-24.04/install.sh

@@ -26,14 +26,15 @@ print_usage() {
     1>&2 echo "usage: $0 [ latest | <date> ]"
     1>&2 echo ""
     1>&2 echo "Dates supported:"
-    1>&2 echo "    2025-Jan-01"
-    1>&2 echo "    2025-Feb-01"
+    1>&2 echo "    2025-Apr-01"
     1>&2 echo "    2025-Mar-01"
+    1>&2 echo "    2025-Feb-01"
+    1>&2 echo "    2025-Jan-01"
 }
 
 if [ $# -eq 0 ]
 then
-    VERSION="2025-Mar-01"
+    VERSION="2025-Apr-01"
     echo "No version specified.  Defaulting to ${VERSION}"
 elif [ $# -eq 1 ]
 then
@@ -62,6 +63,12 @@ case ${VERSION} in
 	export INSTALL_P4C_SOURCE_VERSION="3ffac66ee232f2ab9d1860751dde94725d3b1af8"
 	export INSTALL_PTF_SOURCE_VERSION="77a5ba448f3db54b45a03a6235b7cec8c8c7d093"
 	;;
+    2025-Apr-01)
+	export INSTALL_BEHAVIORAL_MODEL_SOURCE_VERSION="d12eefc7bc19fb4da615b1b45c1235899f2e4fb1"
+	export INSTALL_PI_SOURCE_VERSION="17802cfd67218a26307c0ea69fe520751ca6ab64"
+	export INSTALL_P4C_SOURCE_VERSION="1d456721080836ecf9afc7daaf17147332173620"
+	export INSTALL_PTF_SOURCE_VERSION="e29ef7ec0bd34d4ceef88016383e53238ab5383c"
+	;;
     latest)
 	echo "Using the latest version of all p4lang repository source code."
 	;;