Suggestion: update README/HACKING regarding tests

[Assaf Gordon]

As per: http://lists.gnu.org/archive/html/coreutils/2012-09/msg00144.html ,

Perhaps you'll agree to update README/HACKING about how to run individual tests:
===
diff --git a/HACKING b/HACKING
index de8cd7b..01e7605 100644
--- a/HACKING
+++ b/HACKING
@@ -438,9 +438,11 @@ Nearly every significant change must be accompanied by a 
test suite
 addition that exercises it.  If you fix a bug, add at least one test that
 fails without the patch, but that succeeds once your patch is applied.
 If you add a feature, add tests to exercise as much of the new code
-as possible. Note to run tests/misc/new-test in isolation you can do:
+as possible. If you add a new test file (as opposed to adding a test to an
+existing test file) add the new test file to 'tests/local.mk'.
+Note to run tests/misc/new-test in isolation you can do:
 
-  (cd tests && make check TESTS=misc/new-test VERBOSE=yes)
+  make TESTS=tests/misc/new-test SUBDIRS=. VERBOSE=yes
 
 Variables that are significant for tests with their default values are:
 
diff --git a/README b/README
index 21c9b03..15ed29b 100644
--- a/README
+++ b/README
@@ -176,7 +176,7 @@ in verbose mode for each failing test.  For example,
 if the test that fails is tests/misc/df, then you would
 run this command:
 
-  (cd tests && make check TESTS=misc/df VERBOSE=yes) >> log 2>&1
+  make check TESTS=tests/misc/df SUBDIRS=. VERBOSE=yes >> log 2>&1
 
 For some tests, you can get even more detail by adding DEBUG=yes.
 Then include the contents of the file 'log' in your bug report.
===


Regards,
-gordon