docs: update colors.xml reference (#605)

## What does this change?

Commit 2728211 moved the `colors.xml`
file. This PR adjusts sources to changes.

## Type of change

- [x] Bug fix (non-breaking change which fixes an issue)

------

Signed-off-by: Emmanuel Ferdman <[email protected]>

Author: emmanuel-ferdman

README.md

@@ -511,7 +511,7 @@ Text(
 
 ### Colors
 
-[FlutterGen] supports generating colors from [XML](example/assets/color/colors.xml) format files.  
+[FlutterGen] supports generating colors from [XML](examples/example/assets/color/colors.xml) format files.  
 _Ignore duplicated._
 
 ```yaml