Aligned headline level with try_join section

yuk1ty · yuk1ty · commit 1f3419573c58 · 2023-10-27T16:45:17.000+09:00
diff --git a/src/06_multiple_futures/02_join.md b/src/06_multiple_futures/02_join.md
@@ -3,7 +3,7 @@
 The `futures::join` macro makes it possible to wait for multiple different
 futures to complete while executing them all concurrently.
 
-# `join!`
+## `join!`
 
 When performing multiple asynchronous operations, it's tempting to simply
 `.await` them in a series:
