Proxy documentation: Add a link to new WPAD section.

Change-Id: I57e137fc1dd69429d5e132b5dc8d83fa764ad221
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2147796
Auto-Submit: Eric Roman <eroman@chromium.org>
Reviewed-by: Matt Menke <mmenke@chromium.org>
Commit-Queue: Matt Menke <mmenke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#758535}

net/docs/proxy.md

@@ -956,10 +956,9 @@ _capture ended_.
   * (per-profile) Chrome extensions (ex: [chrome.proxy](https://developer.chrome.com/extensions/proxy))
   * (per-network) System proxy settings
 
-* Was proxy autodetect (WPAD) specified? In this case the final URL probed will
-  be reflected by the difference between the "Effective" and "Original"
-  settings. A known issue with auto-detect is that DHCP based auto-detect is only
-  supported by Chrome running on Windows and Chrome OS.
+* Was [proxy autodetect (WPAD)](#Web-Proxy-Auto_Discovery-WPAD) specified? In
+  this case the final URL probed will be reflected by the difference between
+  the "Effective" and "Original" settings.
 
 * Internally, proxy settings are per-NetworkContext. The proxy
   overview tab shows settings for a *particular* NetworkContext, namely the