message: Improve the wording of `dl` documentation.
diff: @@ -127,12 +127,17 @@ looks like:
  The keys are:
  - `dl`: This is the URL for downloading crates listed in the index. The value
  - may have the markers `{crate}` and `{version}` which are replaced with the
  - name and version of the crate to download, or the marker `{prefix}` which is
  - replaced with the crate's prefix, or the marker `{lowerprefix}` which is
  - replaced with the crate's prefix converted to lowercase. If none of the
  - markers are present, then the value `/{crate}/{version}/download` is appended
  - to the end. See below for more about crate prefixes.
  + may have the following markers which will be replaced with their
  + corresponding value:
  +
  + - `{crate}`: The name of crate.
  + - `{version}`: The crate version.
  + - `{prefix}`: A directory prefix computed from the crate name. For example,
  + a crate named `cargo` has a prefix of `ca/rg`. See below for details.
  + - `{lowerprefix}`: Lowercase variant of `{prefix}`.
  +
  + If none of the markers are present, then the value
  + `/{crate}/{version}/download` is appended to the end.
  - `api`: This is the base URL for the web API. This key is optional, but if it
  is not specified, commands such as [`cargo publish`] will not work. The web
  API is described below.
  