add src/hello.c to augment new command tutorial

The hello module provides the 'hello' command, printing a greetings
to the command console.  It can grow to serve as pedagogical example
of services that OpenOCD developers should use: a runnable style guide.

src/Makefile.am

@@ -12,7 +12,9 @@ endif
 openocd_SOURCES = $(MAINFILE)
 openocd_LDADD = libopenocd.la
 
-libopenocd_la_SOURCES = openocd.c
+libopenocd_la_SOURCES = \
+	hello.c \
+	openocd.c
 
 # set the include path found by configure
 AM_CPPFLAGS = \