Format all instructions.append.md to start with an H1 (required but ignored) and H2

exercises/practice/circular-buffer/.docs/instructions.append.md

@@ -1,4 +1,7 @@
-# Set `errno` to a special value
+# Instructions append
+
+## Set `errno` to a special value
+
 If the buffer is empty during a read attempt, an error is raised to alert the client.
 
 These error values can be found in the [`errno.h`][errno.h] header file.

exercises/practice/gigasecond/.docs/instructions.append.md

@@ -1,3 +1,5 @@
+# Instructions append
+
 ## Use UTC
 
 To solve this problem, you'll need to convert a `time_t` value into a `struct tm` value.

exercises/practice/high-scores/.docs/instructions.append.md

@@ -1,5 +1,7 @@
 # Instructions append
 
+## Implementation
+
 The functions in this exercise accept an array containing one or more numbers, each representing one 'game score'.
 
 The player's game scores can be read from

exercises/practice/word-count/.docs/instructions.append.md

@@ -1,3 +1,5 @@
 # Instructions append
 
-- Note that the tests for this exercise expect the output words to be proper C strings. That is, they should be NUL terminated. See https://en.wikipedia.org/wiki/C_string_handling
+## Implementation
+
+- Note that the tests for this exercise expect the output words to be proper C strings. That is, they should be NUL terminated. See https://en.wikipedia.org/wiki/C_string_handling