Fix text formatting for diff examples

[elfring]

Some places are still improvable in the file “README.md”, aren't they? :thinking:

[elfring]

Thanks for your change acceptance.

:thought_balloon: I find that a few details need further considerations in this document.

• Number of relevant curly brackets in the unified diff example
• Would you like to support customised data colouring for your configuration file instead of using the questionable code type indication “c”?