Add MD hotkeys doc

Usage/hotkeys.md

@@ -6,6 +6,10 @@ icon: key-asterisk
 
 **For the most up-to-date list of HotKeys that will work in your SillyTavern instance, use the `/help hotkeys` slash command in any chat.**
 
+**Hotkeys are disabled for mobile devices.**
+
+## Chat Hotkeys
+
 * Up = Edit last message in chat
 * Ctrl+Up = Edit last USER message in chat
 * Left = swipe left
@@ -17,4 +21,12 @@ icon: key-asterisk
   * *(while editing message AND Message Edit AutoSave is enabled)* = close edit box.
   * *(while an AI message is generating or streaming)* = stop the generation immediately.
 
-**Hotkeys are disabled for mobile devices**
+## Markdown Hotkeys
+
+Needs to be enabled under the "User Settings" tab. Works in the chatbar and textareas marked with the "M↓" icon:
+
+* Ctrl+B = \*\*bold\*\*
+* Ctrl+I = \*italic\*
+* Ctrl+U = \_\_underline\_\_
+* Ctrl+K = \`inline code\`
+* Ctrl+Shift+~ = \~\~strikethrough\~\~