fix typo in README.md (#8)

Author: mhaberler

README.md

@@ -48,7 +48,7 @@ board = ...
 
 ```ini
 [env:development]
-platform = https://github.com/pioarduino/platform-espressif32.git#development
+platform = https://github.com/pioarduino/platform-espressif32.git#develop
 board = ...
 ...
 ```