Update ui_guidelines

Author: Riksu9000

README.md

@@ -21,6 +21,7 @@ InfiniTime is an open-source firmware for the [Pinetime smartwatch](https://www.
  - [How to implement an application](doc/code/Apps.md)
  - [Generate the fonts and symbols](src/displayapp/fonts/README.md)
  - [Creating a stopwatch in Pinetime(article)](https://pankajraghav.com/2021/04/03/PINETIME-STOPCLOCK.html)
+ - [Tips on designing an app UI](doc/ui_guidelines.md)
 
 ### Build, flash and debug
 

doc/ui_guidelines.md

@@ -4,13 +4,10 @@
 - Buttons should generally be at least 50px high
 - Buttons should generally be on the bottom edge
 - Make interactable objects **big**
-- Recommendations for inner padding, aka distance between buttons:
-	- When aligning 4 objects: 4px, e.g. Settings
-	- When aligning 3 objects: 6px, e.g. App list
-	- When aligning 2 objects: 10px, e.g. Quick settings
 - When using a page indicator, leave 8px for it on the right side
 	- It is acceptable to leave 8px on the left side as well to center the content
 - Top bar takes at least 20px + padding
 	- Top bar right icons move 8px to the left when using a page indicator
+- A black background helps to hide the screen border, allowing the UI to look less cramped when utilizing the entire display area.
 
 ![example layouts](./ui/example.png)