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

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

@@ -1,5 +1,7 @@
 # Instructions append
 
+## Unicode and lifetimes
+
 The Rust track extends the possible letters to be any unicode character, not just ASCII alphabetic ones.
 
 You are going to have to adjust the function signature provided in the stub in order for the lifetimes to work out properly.

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

@@ -1,5 +1,7 @@
 # Instructions append
 
+## Efficient Allocation
+
 Note the additional test case in `tests/alloc-attack.rs`. It tests against
 algorithmically inefficient implementations. Because of that, it usually times
 out online instead of outright failing, leading to a less helpful error message.

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

@@ -1,3 +1,5 @@
 # Instructions append
 
+## The time crate
+
 If you're unsure what operations you can perform on `PrimitiveDateTime` take a look at the [time crate](https://docs.rs/time) which is listed as a dependency in the `Cargo.toml` file for this exercise.

exercises/practice/hello-world/.docs/instructions.append.md

@@ -1,3 +1,5 @@
 # Instructions append
 
+## Running tests
+
 In the Rust track, tests are run using the command `cargo test`.

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

@@ -1,3 +1,5 @@
 # Instructions append
 
+## Remainder operation
+
 You may use the [`arithmetic remainder` operator](https://doc.rust-lang.org/book/appendix-02-operators.html) to test for divisibility.

exercises/practice/nth-prime/.docs/instructions.append.md

@@ -1,3 +1,5 @@
 # Instructions append
 
+## Zero based indexing
+
 Remember that while people commonly count with 1-based indexing (i.e. "the 6th prime is 13"), many programming languages, including Rust, use 0-based indexing (i.e. `primes[5] == 13`). Use 0-based indexing for your implementation.

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

@@ -1,5 +1,7 @@
 # Instructions append
 
+## Handling edge cases
+
 Different languages on Exercism have different expectations about what the result should be if the length of the substrings is zero.
 On the Rust track, we don't have a test for that case, so you are free to do what you feel is most appropriate.
 

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

@@ -1,7 +1,9 @@
 # Instructions append
 
+## Bonus tests
+
 To get the bonus tests to run, execute the tests with:
 
 ```bash
 $ cargo test --features exponentials
-```
+```