add description of new option to docs and add option (commented out) into template.

docs/faq_keymap.md

@@ -116,7 +116,9 @@ https://github.com/tekezo/Karabiner/issues/403
 
 ## Esc and `~ on a key
 
-Use `GRAVE_ESC` or `KC_GESC` in your keymap.
+Use `GRAVE_ESC` or `KC_GESC` in your keymap. `GUI`+`GRAVE_ESC` results in `\`` and `SHIFT`+`GRAVE_ESC` results in `~`.
+
+Note that this will break the CTRL+SHIFT+ESC shortcut to the Windows task manager. Use `#define GRAVE_ESC_CTRL_OVERRIDE` in your `config.h` to get the shortcut back. With this option, `ESC_GRAVE` results in `ESC` if `CTRL` is held, even if `SHIFT` or `GUI` are also held.
 
 ## Arrow on Right Modifier keys with Dual-Role
 This turns right modifer keys into arrow keys when the keys are tapped while still modifiers when the keys are hold. In TMK the dual-role function is dubbed **TAP**.

quantum/template/config.h

@@ -67,6 +67,11 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 /* Locking resynchronize hack */
 #define LOCKING_RESYNC_ENABLE
 
+/* If defined, GRAVE_ESC will always act as ESC when CTRL is held.
+ * This is userful for the Windows task manager shortcut (ctrl+shift+esc).
+ */
+// #define GRAVE_ESC_CTRL_OVERRIDE
+
 /*
  * Force NKRO
  *