doc/go1.15: add code tags

Other command line arguments are written in code tags, so add a code tag for consistency.

For #37419

Change-Id: I1948536c3a1860d93726484be2dc7bcb03dfdc2f
Reviewed-on: https://go-review.googlesource.com/c/go/+/237539
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
diff --git a/doc/go1.15.html b/doc/go1.15.html
index f451c1b..d6e238e 100644
--- a/doc/go1.15.html
+++ b/doc/go1.15.html
@@ -50,8 +50,8 @@
 <h3 id="windows">Windows</h3>
 
 <p> <!-- CL 214397 and CL 230217 -->
-  Go 1.15 now generates Windows ASLR executables when -buildmode=pie
-  cmd/link flag is provided. Go command uses -buildmode=pie by default
+  Go 1.15 now generates Windows ASLR executables when <code>-buildmode=pie</code>
+  cmd/link flag is provided. Go command uses <code>-buildmode=pie</code> by default
   on Windows.
 </p>