add color in readme.md git code example
Example 1: how to add color in text github readme
```diff
- text in red
+ text in green
! text in orange
# text in gray
@@ text in purple (and bold)@@
```
Example 2: change text color in md file
-  `#f03c15`
-  `#c5f015`
-  `#1589F0`