HACKING file: proposed addition

[Jim Keniston]

I propose appending the following text to the "test suites" section of
src/HACKING.

  To run a particular test or set of tests, do:
    cd testsuite
    make check RUNTESTFLAGS=subdir/test.exp
  or
    make installcheck RUNTESTFLAGS=subdir/test.exp
  For example:
    make installcheck RUNTESTFLAGS=systemtap.string/strtol.exp

The last paragraph of HACKING says:
  Proposed changes to these guidelines should be discussed on the
  mailing list.
so please discuss away.

Thanks.
Jim