message: Makefile: Correctly document the Apollo3 support
diff: @@ -14,6 +14,7 @@ usage:
  @echo " - opentitan"
  @echo " - hifive1"
  @echo " - nrf52"
  + @echo " - apollo3"
  @echo
  @echo "Run 'make setup' to setup Rust to build libtock-rs."
  @echo "Run 'make <board>' to build libtock-rs for that board"
  