Document headers in practice exercise .append.md files (#592)

Author: IsaacG

building/tracks/practice-exercises/README.md

@@ -178,9 +178,15 @@ A track that doesn't want Bob to support non-ASCII messages, might add the follo
 ```markdown
 # Introduction append
 
+## Note
+
 As part of his teenage rebellion, Bob has decided to only communicate using ASCII.
 ```
 
+Append files should start with an H1 header.
+This header does not get displayed, but should still be present.
+The H1 header is often followed by an H2 header, which helps to separate the generic content from the track specific content.
+
 ### File: `.docs/instructions.md`
 
 **Purpose:** Provide instructions for the exercise.
@@ -224,9 +230,15 @@ In some (rare) cases, you might want to expand on the exercise's `instructions.m
 ```markdown
 # Instructions append
 
+## Note
+
 Bob's conversational partner is a purist when it comes to written communication and always follows normal rules regarding sentence punctuation in English.
 ```
 
+Append files should start with an H1 header.
+This header does not get displayed, but should still be present.
+The H1 header is often followed by an H2 header, which helps to separate the generic content from the track specific content.
+
 ### File: `.docs/hints.md`
 
 **Purpose:** Provide hints to a student to help them get themselves unstuck in an exercise.