Added howto for sending NRST signal through GDB (#776)

See https://github.com/texane/stlink/issues/774

README.md

@@ -113,9 +113,15 @@ Kill the program being debugged? (y or n) y
 Starting program: /home/whitequark/ST/apps/bally/firmware.elf
 ```
 
-Remember that you can shorten the commands. `tar ext :4242' is good enough
+Remember that you can shorten the commands. `tar ext :4242` is good enough
 for GDB.
 
+If you need to send a hard reset signal through `NRST` pin, you can use the following command:
+``
+(gdb) monitor jtag_reset
+```
+
+
 ## Running programs from SRAM
 
 You can run your firmware directly from SRAM if you want to. Just link