Added notes to r2dbc module

Author: velo

querydsl-r2dbc/README.md

@@ -0,0 +1,13 @@
+# R2DBC support
+
+For now, it's highly experimental, looking for feedback!
+
+There will be a serious refactor to eliminate code and test code duplications with querydsl-sql!
+
+Must restore `#addBatch()` functionality, but I don't think I can do it.
+
+```
+$ git revert 9179f4e8e0a2b11af82335a902067583087266fa
+```
+
+Any bugs can be addressed on PRs