Update bootstrap.example.toml

Co-authored-by: Jakub Beránek <[email protected]>

Author: Hayden602

bootstrap.example.toml

@@ -859,7 +859,7 @@
 # Trigger a `DebugBreak` after an internal compiler error during bootstrap on Windows
 #rust.break-on-ice = true
 
-# Set the number of threads used during rustc compilation
+# Set the number of threads for the compiler frontend used during rustc compilation (passed to `-Zthreads`).
 # The valid options are:
 # 1 - Use non-parallel compilation
 # N - Number of threads used for rustc compilation