ruff server: Add tracing setup guide to Neovim documentation (#11884)

A follow-up to [this
suggestion](#11747 (comment))
on the tracing PR.

---------

Co-authored-by: Dhruv Manilawala <[email protected]>

Author: snowsignal

Diff for: crates/ruff_server/docs/setup/NEOVIM.md

@@ -54,3 +54,39 @@ require('lspconfig').pyright.setup {
   },
 }
 ```
+
+By default, Ruff will not show any logs. To enable logging in Neovim, you'll need to set the `RUFF_TRACE` environment variable
+to either `messages` or `verbose`:
+
+```lua
+require('lspconfig').ruff.setup {
+  cmd_env = { RUFF_TRACE = "messages" }
+}
+```
+
+You can set the log level in `settings`:
+
+```lua
+require('lspconfig').ruff.setup {
+  cmd_env = { RUFF_TRACE = "messages" },
+  init_options = {
+    settings = {
+      logLevel = "debug",
+    }
+  }
+}
+```
+
+It's also possible to divert Ruff's logs to a separate file with the `logFile` setting:
+
+```lua
+require('lspconfig').ruff.setup {
+  cmd_env = { RUFF_TRACE = "messages" },
+  init_options = {
+    settings = {
+      logLevel = "debug",
+      logFile = "your/log/file/path/log.txt"
+    }
+  }
+}
+```