docs: update README.md to note that cargo workspaces need a manifest …

…driven release (#2001)

fix #1998.

Co-authored-by: Jeff Ching <chingor@google.com>

README.md

@@ -187,7 +187,7 @@ Release Please automates releases for the following flavors of repositories:
 | `php`               | A repository with a composer.json and a CHANGELOG.md |
 | `python`            | [A Python repository, with a setup.py, setup.cfg, CHANGELOG.md](https://github.com/googleapis/python-storage) and optionally a pyproject.toml and a <project>/\_\_init\_\_.py |
 | `ruby`              | A repository with a version.rb and a CHANGELOG.md |
-| `rust`              | A Rust repository, with a Cargo.toml (either as a crate or workspace) and a CHANGELOG.md |
+| `rust`              | A Rust repository, with a Cargo.toml (either as a crate or workspace, although note that workspaces require a [manifest driven release](https://github.com/googleapis/release-please/blob/main/docs/manifest-releaser.md) and the "cargo-workspace" plugin) and a CHANGELOG.md |
 | `sfdx`              | A repository with a [sfdx-project.json](https://developer.salesforce.com/docs/atlas.en-us.sfdx_dev.meta/sfdx_dev/sfdx_dev_ws_config.htm) and a CHANGELOG.md |
 | `simple`            | [A repository with a version.txt and a CHANGELOG.md](https://github.com/googleapis/gapic-generator) |
 | `terraform-module`  | [A terraform module, with a version in the README.md, and a CHANGELOG.md](https://github.com/terraform-google-modules/terraform-google-project-factory) |