cabana: add usage to readme

tools/cabana/README.md

@@ -6,4 +6,19 @@ Cabana is a tool developed to view raw CAN data. One use for this is creating an
 
 ## Usage Instructions
 
+```bash
+$ ./cabana -h
+Usage: ./_cabana [options] route
+
+Options:
+  -h, --help             Displays this help.
+  --demo                 use a demo route instead of providing your own
+  --qcam                 load qcamera
+  --data_dir <data_dir>  local directory with routes
+
+Arguments:
+  route                  the drive to replay. find your drives at
+                         connect.comma.ai
+```
+
 See [openpilot wiki](https://github.com/commaai/openpilot/wiki/Cabana)