Merge branch 'pb/test-scripts-are-build-targets'

The t/README file now gives a hint on running individual tests in
the "t/" directory with "make t<num>-*.sh t<num>-*.sh".

* pb/test-scripts-are-build-targets:
  t/README: mention test files are make targets

Author: gitster

t/README

@@ -32,6 +32,13 @@ the tests.
     ok 2 - plain with GIT_WORK_TREE
     ok 3 - plain bare
 
+t/Makefile defines a target for each test file, such that you can also use
+shell pattern matching to run a subset of the tests:
+
+    make *checkout*
+
+will run all tests with 'checkout' in their filename.
+
 Since the tests all output TAP (see https://testanything.org) they can
 be run with any TAP harness. Here's an example of parallel testing
 powered by a recent version of prove(1):