doc/go1.15: 1.15 supports OpenBSD 6.7 on arm and arm64

Change-Id: Ibea6fbb73abdb7201855e80967120c07484d6460
Reviewed-on: https://go-review.googlesource.com/c/go/+/236557
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/doc/go1.15.html b/doc/go1.15.html
index bdb327e..15f56ee 100644
--- a/doc/go1.15.html
+++ b/doc/go1.15.html
@@ -69,6 +69,15 @@
 	planned to become the default NDK linker in a future NDK version.
 </p>
 
+<h3 id="openbsd">OpenBSD</h3>
+
+<p><!-- CL 234381 -->
+  Go 1.15 adds support for OpenBSD 6.7 on <code>GOARCH=arm</code>
+  and <code>GOARCH=arm64</code>. Previous versions of Go already
+  supported OpenBSD 6.7 on <code>GOARCH=386</code>
+  and <code>GOARCH=amd64</code>.
+</p>
+
 <h3 id="riscv">RISC-V</h3>
 
 <p>