[zx] Generate syscall documentation

This change wires up the zither syscall documentation backend to the
build, registering all markdown pages as goldens: the upshot of this is
that regeneration will happen automatically when building.

Bug: 118025
Change-Id: If5362e43c85ed6f6c8186ebc9eaee65786408148
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/781423
Reviewed-by: Brett Wilson <brettw@google.com>
Fuchsia-Auto-Submit: Joshua Seaton <joshuaseaton@google.com>
Reviewed-by: Roland McGrath <mcgrathr@google.com>
Commit-Queue: Auto-Submit <auto-submit@fuchsia-infra.iam.gserviceaccount.com>
diff --git a/docs/reference/syscalls/timer_create.md b/docs/reference/syscalls/timer_create.md
index 3f12737..4fb4618 100644
--- a/docs/reference/syscalls/timer_create.md
+++ b/docs/reference/syscalls/timer_create.md
@@ -1,4 +1,14 @@
-<!-- Generated by zircon/scripts/update-docs-from-fidl, do not edit! -->
+<!--
+Copyright 2022 The Fuchsia Authors. All rights reserved.
+Use of this source code is governed by a BSD-style license that can be
+found in the LICENSE file.
+
+DO NOT EDIT. Generated from FIDL library zx by zither, a Fuchsia platform tool.
+
+See //docs/reference/syscalls/README.md#documentation-generation for
+regeneration instructions.
+-->
+
 # zx_timer_create
 
 ## Summary
@@ -69,4 +79,3 @@
 [`zx_handle_close()`]: handle_close.md
 [`zx_timer_cancel()`]: timer_cancel.md
 [`zx_timer_set()`]: timer_set.md
-