docs(README): npm test watches files for changes

Author: petebacondarwin

README.md

@@ -105,13 +105,17 @@ The easiest way to run the unit tests is to use the supplied npm script:
 npm test
 ```
 
-This script will start the Karma test runner to execute the unit tests.
+This script will start the Karma test runner to execute the unit tests. Moreover, Karma will sit and
+watch the source and test files for changes and then re-run the tests whenever any of them change.
+This is the recommended strategy; if you unit tests are being run every time you save a file then
+you receive instant feedback on any changes that break the expected code functionality.
 
-We can also have Karma sit and watch the application and test files for changes and re-run the
-tests whenever any of them change.  You can do this with:
+You can also ask Karma to do a single run of the tests and then exit.  This is useful if you want to
+check that a particular version of the code is operating as expected.  The project contains a
+predefined script to do this:
 
 ```
-npm run test-watch
+npm run test-single-run
 ```