[readme] Add link to tape-player (in-process reporter) (#496)

readme.markdown

@@ -134,6 +134,7 @@ By default, uncaught exceptions in your tests will not be intercepted, and will
 - Different test syntax with https://github.com/pguth/flip-tape (warning: mutates String.prototype)
 - Electron test runner with https://github.com/tundrax/electron-tap
 - Concurrency support with https://github.com/imsnif/mixed-tape
+- In-process reporting with https://github.com/DavidAnson/tape-player
 
 # methods