mk: Add tidy commands to 'make tips'

Author: brson

Makefile.in

@@ -59,6 +59,9 @@
 #   * check-stage$(stage)-$(crate) - Test a crate in a specific stage
 #   * check-stage$(stage)-{rpass,rfail,cfail,rmake,...} - Run tests in src/test/
 #   * check-stage1-T-$(target)-H-$(host) - Run cross-compiled-tests
+#   * tidy-basic - show file / line stats
+#   * tidy-errors - show the highest rustc error code
+#   * tidy-features - show the status of language and lib features
 #
 # Then mix in some of these environment variables to harness the
 # ultimate power of The Rust Build System.