Document how to get code coverage. (#339)

* Document how to get code coverage.

Change-Id: If7eae6008ad0394490885f88b6edb8436d9f54f3

* Remove (hopefully insignificant) whitespace.

Change-Id: Ie4079dd2998c616ae5b6e5b031e29cea5f11d9f8

Author: timsifive

HACKING

@@ -77,6 +77,32 @@ patch:
   src/openocd -s ../tcl -f /path/to/openocd.cfg
   @endcode
 
+- Runtime coverage testing
+
+  Apply the following patch to prevent OpenOCD from killing itself:
+  @code
+--- a/src/openocd.c
++++ b/src/openocd.c
+@@ -372,8 +372,6 @@ int openocd_main(int argc, char *argv[])
+
+        if (ERROR_FAIL == ret)
+                return EXIT_FAILURE;
+-       else if (ERROR_OK != ret)
+-               exit_on_signal(ret);
+
+        return ret;
+ }
+  @endcode
+
+  Configure your OpenOCD binary with coverage support as follows:
+  @code
+  LDFLAGS="-fprofile-arcs -ftest-coverage"
+		   CFLAGS="-fprofile-arcs -ftest-coverage" ./configure
+  @endcode
+
+  Now every time OpenOCD is run, coverage info in your build directory is
+  updated. Running `gcov src/path/file.c` will generate a report.
+
 Please consider performing these additonal checks where appropriate
 (especially Clang Static Analyzer for big portions of new code) and
 mention the results (e.g. "Valgrind-clean, no new Clang analyzer