README.md: document BASESUITE variable

.gitlab-ci.yml

@@ -137,7 +137,7 @@ build_linux:
       - changes
       - linux/linux_*_arm64-*.build
   script: |
-    runuser -u build -- sh -xc '. ./common.sh; cd linux; . ./build.sh' 2>&1 | ./filter-output
+    runuser -u build -- sh -xc '. ./common.sh; cd linux; export BASESUITE=unstable; . ./build.sh' 2>&1 | ./filter-output
     dpkg-deb -c changes/linux-image-*-reform2-arm64_*_arm64.deb | grep 'kernel/drivers/gpu/drm/imx\(/cdns\)\?/cdns_mhdp_imx.ko'
     echo "BASESUITE: $BASESUITE"
     echo "OURSUITE: $OURSUITE"

README.md

@@ -66,3 +66,8 @@ Scripts for running the reform.
 To just rebuild the kernel and not the rest, you can run this:
 
     sh -xc '. ./setup.sh; cd linux; . ./build.sh'
+
+You can also build the kernel of a specific suite by setting `BASESUITE` to the
+suite name like `experimental` in this example:
+
+    sh -xc 'BASESUITE=experimental; . ./setup.sh; cd linux; . ./build.sh'