minor doc updates

docs/en/config_and_keymap.md

@@ -72,6 +72,14 @@ print(dir(board))
 keyboard.keymap = [[KC.A, KC.B]]
 ```
 
+- The keymap contains a flat list of `Key` objects for each layer of the keyboard.
+  The list of keys in each layer are stored as a single list that folllows the 
+  grid of row and column pins in the keyboard matrix.  This list starts with keys 
+  in the first row from left to right, then the second row, and so on.  
+  The row x column matrix structure doesn't appear explicitly
+  in the keymap.  Use `KC.NO` to mark grid positions without a physical key.
+  For very sparse grids `keyboard.coord_mapping` can be useful to avoid `KC.NO`. 
+
 You can further define a bunch of other stuff:
 
 - `keyboard.debug_enabled` which will spew a ton of debugging information to the serial

docs/en/holdtap.md

@@ -1,6 +1,18 @@
 # HoldTap Keycodes
-Enabling HoldTap will give you access to the following keycodes and can simply be
-added to the modules list.
+The HoldTap module lets keys do double duty:
+tap the key to do one thing, 
+hold it longer than the configurable `tap_time` to do another.
+
+HoldTap is often used with modifier keys.
+For example `KC.HT(KC.ESCAPE, KC.LCTRL)` configures 
+a key that sends Escape when tapped and 
+left control when held.  
+It can be used with regular keys as well
+like `KC.HT(KC.SPACE, KC.ENTER)` to send space on tab
+and enter on hold.
+
+Simply import HoldTap and add it to the modules list.  
+This lets you use `KC.HT` actions like those below.
 
 ```python
 from kmk.modules.holdtap import HoldTap