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

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

@@ -1,5 +1,7 @@
 # Instructions append
 
+## Implementation
+
 In Forth functions are called `words`, they operate on a data stack.
 Each word takes its parameter(s) from the stack and return its result(s) on the stack.
 

exercises/practice/line-up/.docs/instructions.append.md

@@ -1,5 +1,7 @@
 # Instructions append
 
+## Implementation
+
 In this exercise you will implement a procedure which is meant to allocate the string it returns. Deallocating the string is the responsibility of the prodecure's caller.
 
 ```odin

exercises/practice/list-ops/.docs/instructions.append.md

@@ -1,5 +1,7 @@
 # Instructions append
 
+## Implementation
+
 You will need to use Odin parameter polymorphism (more commonly called generics) for this exercise .
 If you haven't seen this feature before, here is a quick run-down to get you started.
 

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

@@ -1,5 +1,7 @@
 # Instructions append
 
+## Implementation
+
 In this exercise you will implement a procedure which is meant to allocate the string it returns. Deallocating the string is the responsibility of the prodecure's caller.
 
 ```odin

exercises/practice/relative-distance/.docs/instructions.append.md

@@ -1,3 +1,5 @@
 # Instructions append
 
+## Implementation
+
 In Odin, if two individuals are not connected, we will return the value -1.