Update GUIDELINES.md

GUIDELINES.md

@@ -87,10 +87,14 @@ If something is really unintelligible and can't be understood even with a bit of
 
 ### 🇩🇪 German
 
-Wir verwenden die **neue deutsche Rechtschreibung**.
+We use **neue deutsche Rechtschreibung**.
 
-#### Elisions, contractions
-    
+#### Apostrophes
+
+We follow the rules from [Duden](https://www.duden.de/sprachwissen/rechtschreibregeln/apostroph) but made a few additional rules to improve consistency:
+
+1. At the end of a word, when an -e is omitted, we generally use apostrophes **except in the case of imperatives**. Example: `Komm her!` but `Ich komm' her`. See rule [D13/2](https://www.duden.de/sprachwissen/rechtschreibregeln/apostroph#D13)
+2. Contractions with `e` in the middle of a word. We apply the rules See rule [D13/1](https://www.duden.de/sprachwissen/rechtschreibregeln/apostroph#D13) in many cases except for when its harder to read: `seh'n` but `verstehn`.
 
 ### 🇫🇷 French