Adding keyboard PR instruction. (#507)

- #502

README.md

@@ -147,6 +147,7 @@ I'd be happy to accept additions to add more languages, and layouts. To start:
   - Change the characters to whatever you'd like.
   - This file contains both a _shifted_, and _non-shifted_ keyboard, so make sure you take care of both.
   - You can also add or subtract columns if you want, but the layout must remain a grid. I **highly recommend** sticking with the 3x3 layout.
+- Add the new keyboard to the [KeyboardLayout.kt file](https://github.com/dessalines/thumb-key/blob/main/app/src/main/java/com/dessalines/thumbkey/utils/KeyboardLayout.kt), with a new higher index.
 - Either open a pull request, or an issue, linking your new keyboard file. I'll handle the rest of the work.
 
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