document build.clippy-driver and build.cargo-clippy options

Signed-off-by: onur-ozkan <work@onurozkan.dev>

config.example.toml

@@ -230,6 +230,18 @@
 # use this rustfmt binary instead as the stage0 snapshot rustfmt.
 #rustfmt = "/path/to/rustfmt"
 
+# Instead of downloading the src/stage0 version of cargo-clippy specified,
+# use this cargo-clippy binary instead as the stage0 snapshot cargo-clippy.
+#
+# Note that this option must be used together with `clippy-driver` below.
+#cargo-clippy = "/path/to/cargo-clippy"
+
+# Instead of downloading the src/stage0 version of clippy-driver specified,
+# use this clippy-driver binary instead as the stage0 snapshot clippy-driver.
+#
+# Note that this option must be used together with `cargo-clippy` above.
+#clippy-driver = "/path/to/clippy-driver"
+
 # Whether to build documentation by default. If false, rustdoc and
 # friends will still be compiled but they will not be used to generate any
 # documentation.