maint: mention how to run a single test in HACKING docs

* HACKING: Give an example of how to run a test in isolation.
* README: Fix/simplify example for running a single test.
* README-hacking: Reference the HACKING file.

HACKING

@@ -288,7 +288,9 @@ 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.
+as possible. Note to run tests/misc/newtest in isolation you can do:
+
+  (cd tests && make check TESTS=misc/newtest VERBOSE=yes)
 
 There are hundreds of tests in the tests/ directories.  You can use
 tests/sample-test as a template, or one of the various Perl-based ones

README

@@ -161,17 +161,13 @@ Reporting bugs:
 IMPORTANT: if you take the time to report a test failure,
 please be sure to include the output of running `make check'
 in verbose mode for each failing test.  For example,
-if the test that fails is tests/mv/hard-link-1, then you
-would run this command:
+if the test that fails is tests/misc/df, then you would
+run this command:
 
-  env VERBOSE=yes make check -C tests/mv TESTS=hard-link-1 >> log 2>&1
+  (cd tests && make check TESTS=misc/df VERBOSE=yes) >> log 2>&1
 
-For some tests, you can get even more detail by including
-DEBUG=yes in the environment:
-
-  env DEBUG=yes VERBOSE=yes make check -C tests/mv TESTS=hard-link-1 >> log 2>&1
-
-and then include the contents of the file `log' in your bug report.
+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.
 
 ***************************************
 

README-hacking

@@ -2,6 +2,7 @@
 
 These notes intend to help people working on the checked-out sources.
 These requirements do not apply when building from a distribution tarball.
+See also HACKING for more detailed coreutils contribution guidlines.
 
 * Requirements