message: add instructions for building a local package
diff: @@ -89,6 +89,11 @@ docker-compose run web build crate <CRATE_NAME> <CRATE_VERSION>
  # Builds every crate and adds them into database
  # (beware: this may take months to finish)
  docker-compose run web build world
  +
  +# Builds a local package you have at <SOURCE> and adds it to the database.
  +# The package does not have to be on crates.io.
  +# The package must be on the local filesystem, git urls are not allowed.
  +docker-compose run -v "$(realpath <SOURCE>)":/build web build crate --local /build
  ```
  