dashboard/app: make static resources work for dev_appserver.py

The production app sets CWD to the root of the syzkaller repository,
so paths that refer to static resources in app.yaml look like dashboard/app/static/*.
However, dev_appserver.py sets CWD to dashboard/app, so these paths do not work.
Add soft link dashboard/app/dashboard/app/static that point to dashboard/app/static,
so that dashboard/app/static/* paths work from both locations.

Author: dvyukov

dashboard/app/dashboard/README.md

@@ -0,0 +1,6 @@
+This dir exists for the purposes of running the dashboard app locally using dev_appserver.py.
+The production app sets CWD to the root of the syzkaller repository, so paths that refer to
+static resources in app.yaml look like dashboard/app/static/*. However, dev_appserver.py
+sets CWD to dashboard/app, so these paths do not work. This dir contains soft link
+dashboard/app/dashboard/app/static that point to dashboard/app/static, so that
+dashboard/app/static/* paths work from both locations.

dashboard/app/dashboard/app/static

@@ -0,0 +1 @@
+../../static