Add reference to Nu Plugin Tracer in the Nushell Book. (#1372)

* Add reference to Nu Plugin Tracer in the Nushell Book.

* Rename nu_plugin_tracer as trace_nu_plugin

* Add trace output accumulation warning inline

Its also in the README for trace_nu_plugin

* Refer to plugin rm to remove plugin

Co-authored-by: Darren Schroeder <[email protected]>

---------

Co-authored-by: Darren Schroeder <[email protected]>

Author: tesujimath

book/plugins.md

@@ -170,6 +170,12 @@ Nu's main repo contains example plugins that are useful for learning how the plu
 
 The simplest way to debug a plugin is to print to stderr; plugins' standard error streams are redirected through Nu and displayed to the user.
 
+### Tracing
+
+The Nu plugin protocol message stream may be captured for diagnostic purposes using [trace_nu_plugin](https://crates.io/crates/trace_nu_plugin/).
+
+**WARNING: trace output will accumulate for as long as the plugin is installed with the trace wrapper.  Large files are possible.  Be sure to remove the plugin with `plugin rm` when finished tracing, and reinstall without the trace wrapper.**
+
 ## Help
 
 Nu's plugin documentation is a work in progress. If you're unsure about something, the #plugins channel on [the Nu Discord](https://discord.gg/NtAbbGn) is a great place to ask questions!