Create test-templates/README (arkworks-rs#585)

re-direct the confused user to the appropriate way of testing arkworks

Author: mmaker

test-templates/README.md

@@ -0,0 +1,4 @@
+# test-templates
+
+**Warning!!!** This package does not implement any tests, but exports templates and macros for testing.
+In order to test arkworks, please run `cargo test` inside [algebra](https://github.com/arkworks-rs/algebra).