dashboard,browser: do not call get_user_config_dir() in argparse

This caused two problems when building the docs:
* the path printed in the docs depends on the machine where they are built
* it pollutes ~/.config, and also breaks Nix builds

artiq/frontend/artiq_browser.py

@@ -20,10 +20,8 @@ logger = logging.getLogger(__name__)
 
 
 def get_argparser():
-    default_db_file = os.path.join(get_user_config_dir(), "artiq_browser.pyon")
-
     parser = argparse.ArgumentParser(description="ARTIQ Browser")
-    parser.add_argument("--db-file", default=default_db_file,
+    parser.add_argument("--db-file", default=None,
                         help="database file for local browser settings "
                         "(default: %(default)s)")
     parser.add_argument("--browse-root", default="",
@@ -132,6 +130,8 @@ class Browser(QtWidgets.QMainWindow):
 def main():
     # initialize application
     args = get_argparser().parse_args()
+    if args.db_file is None:
+        args.db_file = os.path.join(get_user_config_dir(), "artiq_browser.pyon")
     widget_log_handler = log.init_log(args, "browser")
 
     app = QtWidgets.QApplication(["ARTIQ Browser"])

artiq/frontend/artiq_dashboard.py

@@ -36,9 +36,7 @@ def get_argparser():
         help="TCP port to connect to for broadcasts")
     parser.add_argument(
         "--db-file", default=None,
-        help="database file for local GUI settings, "
-             "by default in {} and dependant on master hostname".format(
-                                                        get_user_config_dir()))
+        help="database file for local GUI settings")
     add_common_args(parser)
     return parser
 

doc/manual/faq.rst

@@ -107,3 +107,9 @@ The core device tests require the following TTL devices and connections:
 * ``loop_clock_in``: any input-capable TTL. Must be physically connected to ``loop_clock_out``.
 
 If TTL devices are missing, the corresponding tests are skipped.
+
+find the dashboard and browser configuration files are stored?
+--------------------------------------------------------------
+
+::
+  python -c "from artiq.tools import get_user_config_dir; print(get_user_config_dir())"