HOWTO: Add a reference to Harbison and Steele

Add a reference to Harbison and Steele's C book.
Signed-off-by: Robert P. J. Day <rpjday@mindspring.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

Documentation/HOWTO

@@ -30,6 +30,7 @@ are not a good substitute for a solid C education and/or years of
 experience, the following books are good for, if anything, reference:
  - "The C Programming Language" by Kernighan and Ritchie [Prentice Hall]
  - "Practical C Programming" by Steve Oualline [O'Reilly]
+ - "C:  A Reference Manual" by Harbison and Steele [Prentice Hall]
 
 The kernel is written using GNU C and the GNU toolchain.  While it
 adheres to the ISO C89 standard, it uses a number of extensions that are