plotjuggler readme: refer to openpilot env setup (#25609)

* plotjuggler readme: refer to openpilot env setup

* Update tools/plotjuggler/README.md

Co-authored-by: Shane Smiskol <shane@smiskol.com>

Co-authored-by: Shane Smiskol <shane@smiskol.com>

tools/plotjuggler/README.md

@@ -4,7 +4,7 @@
 
 ## Installation
 
-Once you've cloned and are in openpilot, this command will download PlotJuggler and install our plugins:
+Once you've [set up the openpilot environment](../README.md), this command will download PlotJuggler and install our plugins:
 
 `cd tools/plotjuggler && ./juggle.py --install`