Correct capitalization in README.md

This commit updates the capitalization in a sentence in the README.md file. The sentence now starts with a capital letter, improving readability and adherence to proper grammar.

Author: koriym

README.md

@@ -52,7 +52,7 @@ $ composer require --dev smeghead/php-class-diagram
 ```
 
 Now, you can execute `./vendor/bin/php-class-diagram`.
-for instance, try to display help message.
+For instance, try to display help message.
 
 ```bash
 $ vendor/bin/php-class-diagram --help