slapos-sr-testing: add comment to explain where to list SR

See merge request nexedi/slapos!968

software/slapos-sr-testing/software-py3.cfg

@@ -12,6 +12,7 @@ extra-eggs +=
 
 [template]
 extra =
+# The following list is for SR whose buildout runs only with Python 3.
   helloworld ${slapos.test.helloworld-setup:setup}
   jupyter ${slapos.test.jupyter-setup:setup}
   monitor ${slapos.test.monitor-setup:setup}

software/slapos-sr-testing/software.cfg

@@ -284,11 +284,20 @@ context =
 
 tests =
   json-schemas ${slapos.cookbook-setup:setup}
+# The following list is for SR that work with either Python 2 and 3
+# (as main Python). The test egg must supply a URL which depends on
+# the version of Python that is used to run the test.
+# Due to a bug in the way promises are run, we may also list some Py3-only SR
+# here, to check there's no promise issue when slapos node runs with Python 2.
   kvm ${slapos.test.kvm-setup:setup}
   slaprunner ${slapos.test.slaprunner-setup:setup}
   metabase ${slapos.test.metabase-setup:setup}
+###
   ${:extra}
+
 extra =
+# WARNING: This is for SR that only support Python 2.
+#          You should not add more lines here.
   backupserver ${slapos.test.backupserver-setup:setup}
   caddy-frontend ${slapos.test.caddy-frontend-setup:setup}
   erp5 ${slapos.test.erp5-setup:setup}