Updated Keymap examples (markdown)

Keymap-examples.md

@@ -13,4 +13,25 @@ Keymap code on Alps64
 https://github.com/thisisshi/tmk_keyboard/blob/15fe63e8d181a8a95988dcc71929f0024df55caa/keyboard/alps64/keymap_pure.c
 
 and guide.
-https://github.com/thisisshi/tmk_keyboard/blob/77ac0805ade565fb23657e3644c920ada71edccf/keyboard/alps64/Guide.md
+https://github.com/thisisshi/tmk_keyboard/blob/77ac0805ade565fb23657e3644c920ada71edccf/keyboard/alps64/Guide.md
+
+## Prevent stuck modifiers
+
+Consider the following scenario:
+
+1. Layer 0 has a key defined as Shift.
+2. The same key is defined on layer 1 as the letter A.
+3. User presses Shift.
+4. User switches to layer 1 for whatever reason.
+5. User releases Shift, or rather the letter A.
+6. User switches back to layer 0.
+
+Shift was actually never released and is still considered pressed.
+
+If such situation bothers you add this to your `config.h`:
+
+    #define PREVENT_STUCK_MODIFIERS
+
+This option uses 5 bytes of memory per every 8 keys on the keyboard
+rounded up (5 bits per key). For example on Planck (48 keys) it uses
+(48/8)\*5 = 30 bytes.