docs: warn about upload timeout

Author: tompscanlan

src/doc/man/cargo-publish.md

@@ -22,8 +22,11 @@ following steps:
    - Checks the `package.publish` key in the manifest for restrictions on
      which registries you are allowed to publish to.
 2. Create a `.crate` file by following the steps in {{man "cargo-package" 1}}.
-3. Upload the crate to the registry. Note that the server will perform
-   additional checks on the crate.
+3. Upload the crate to the registry. The server will perform additional
+   checks on the crate. 
+4. The client will poll waiting for the package to appear in the index,
+   and may timeout. In that case, you will need to check for completion
+   manually. This timeout does not affect the upload.
 
 This command requires you to be authenticated with either the `--token` option
 or using {{man "cargo-login" 1}}.