Document the run_tests script

run_tests.in

@@ -1,4 +1,12 @@
 #!/usr/bin/env bash
+#
+# This is a wrapper to allow BDR to run pg_regress etc with a custom
+# config file, the needed extensions installed, etc. It works around the
+# lack of needed pg_regress features in 9.4.
+#
+# Don't call this directly, use "make regresscheck", "make isolationcheck", etc
+# or just "make check"
+# 
 
 set -e
 #set -x