Add files.watcherExlude to vscode.md

I had the issue that vscode didn't notice file changes e.g.
by git cl format. Excluding out/ and third_party/ with
files.watcherExclude seems to help.

Files per folder:
10934 v8
14436 native_client
17478 data
26470 build
37676 chrome
389528 third_party
426532 out

BUG=

Review-Url: https://codereview.chromium.org/2847723002
Cr-Commit-Position: refs/heads/master@{#467668}

docs/vscode.md

@@ -191,6 +191,14 @@ Remember to replace `<full_path_to_your_home>`!
     "out*/**": true
   },
 
+  "files.watcherExclude": {
+    // Don't check out/ and third_party/ for changes to fix issue
+    // where vscode doesn't notice that files have changed.
+    // https://github.com/Microsoft/vscode/issues/3998
+    "**/out/**": true,
+    "**/third_party/**": true
+  },
+
   // Wider author column for annotator extension.
   "annotator.annotationColumnWidth": "24em",