README: add note about Ssreflect and bullets

README

@@ -7,6 +7,11 @@ This version is known to compile with:
  - Ssreflect 1.6
  - Autosubst 1.4
 
+For development, better make sure you have a version of Ssreflect that includes commit be724937
+(no such version has been released so far, you'll have to fetch the development branch yourself).
+Iris compiles fine even without this patch, but proof bullets will only be in 'strict' (enforcing)
+mode with the fixed version of Ssreflect.
+ 
 BUILDING INSTRUCTIONS
 ---------------------