Create mod-tap-tapdance.md (#53)

Add information where to find mod-tap and how to use it vs tap dance.

docs/manual/mod-tap-tapdance.md

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+---
+layout: default
+title: Mod Tap or Quantum vs Tap Dance
+parent: User manual
+nav_order: 8
+---
+
+# Tap Dance is a very powerful tool
+**In fact, it's all too powerful for some simple functions.** Like holding a key for a modifier instead of the normal character, is entirely overkill to implement with a Tap Dance. Especially when that basic function is already there in QMK/Vial in a much simpler format called Mod Tap.
+
+Under the `Keymap -> Quantum` tab you can find a long list of keycodes that create the exact scenario above, where you have a modifier on hold, and then select your desired 'normal' key-code for tapping. 
+
+Please read more in QMK Documentation : [Mod Tap](https://docs.qmk.fm/#/mod_tap?id=mod-tap)