_content/doc/comment: document removal of common prefix

Fixes golang/go#61373

Change-Id: I60fa1be13cb7e32af5169e303f5e1c40d207edc4
Reviewed-on: https://go-review.googlesource.com/c/website/+/524039
Reviewed-by: Russ Cox <rsc@golang.org>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
diff --git a/_content/doc/comment.md b/_content/doc/comment.md
index f945ecf..1c9cd67 100644
--- a/_content/doc/comment.md
+++ b/_content/doc/comment.md
@@ -497,6 +497,8 @@
 `//toolname:directive`.
 
 Gofmt removes leading and trailing blank lines in doc comments.
+If all lines in a doc comment begin with the same sequence of
+spaces and tabs, gofmt removes that prefix.
 
 ### Paragraphs {#paragraphs}