Move docs/ to docs/en/

It allows comparison between the directories and helps translations.

docs/en/sticky_mod.md

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+# Sticky Mod
+This module allows to hold a modifier while a key is being tapped repeatedly; the modifier will be released when any other key is pressed or released.
+This is for example useful if you want to switch between open windows with ALT+TAB or CMD+TAB, using only a single key.
+
+## Enabling the module
+```python
+from kmk.modules.sticky_mod import StickyMod
+sticky_mod = StickyMod()
+keyboard.modules.append(sticky_mod)
+keyboard.keymap = [
+    [
+        KC.SM(kc=KC.TAB, mod=KC.LALT),
+        KC.SM(KC.TAB, KC.LSFT(KC.LALT)),
+    ],
+]
+```
+
+## Keycodes
+
+|Key                      |Description                                    |
+|-------------------------|-----------------------------------------------|
+|`KC.SM(KC.key, KC.mod)`  |sticky mod                                     |