Update README.md

Fixes #386

README.md

@@ -26,10 +26,12 @@ load("@io_bazel_rules_webtesting//web:repositories.bzl", "web_test_repositories"
 web_test_repositories()
 ```
 
-You can use the predefined browsers in `@io_bazel_rules_webtesting//browsers` by
-adding (note we keep versioned browser definitions here, so users can separate
-updating browser versions from updating the version of rules_webtesting they
-use):
+We maintain predefined versioned browsers in 
+`@io_bazel_rules_webtesting//web/versioned:browsers-<version>.bzl` that can be
+referenced from `@io_bazel_rules_webtesting//browsers`. Note: these versions
+in these files are not locked in until the corresponding release has been created.
+
+To use, add the following to your WORKSPACE file:
 
 ```bzl
 load("@io_bazel_rules_webtesting//web/versioned:browsers-<version>.bzl", "browser_repositories")