Improve docs around enabling workspaces

The current README.md makes it sound like using workspaces is required.
If the root crate does not enable workspaces, then cargo-fuzz works
without any changes.

README.md

@@ -25,7 +25,7 @@ $ cargo install -f cargo-fuzz
 
 Initialize a `cargo fuzz` project for your crate!
 
-### Add `fuzz` directory to `workspace.members` in root `Cargo.toml`
+### If your crate uses cargo workspaces, add `fuzz` directory to `workspace.members` in root `Cargo.toml`
 
 `fuzz` directory can be either a part of an existing workspace (default)
 or use an independent workspace. If latter is desired, you can use