Update README.md

Author: alexeagle

README.md

@@ -3,3 +3,4 @@ Replacement for the 'bazel coverage' command:
 - we don't accidentally bust the analysis cache with 'coverage' flags differing from 'test'
 - forget having a Bazel-specific, Java-based, unmaintained LCOV merger and 'combined report' - that never should have been Bazel's job
 - developers really need git-aware diff to show "incremental coverage" - which of the lines I added or modified are covered by tests?
+- ability to add other enforcement thresholds