add explanation how to fully erase bash shell history

based on http://unix.stackexchange.com/questions/203290/how-do-i-clear-the-terminal-history/203295#203295

pages/common/history.md

@@ -6,6 +6,10 @@
 
 `history`
 
-- Clear the commands history list (only for `bash`):
+- Clear the commands history list (only for current `bash` shell):
 
 `history -c`
+
+- Overwrite history file with history of current `bash` shell (typically combined with `history -c` to completely erase history):
+
+`history -w`