update action.yml

Signed-off-by: Magnus Markling <magnus@markling.com>

action.yml

@@ -30,7 +30,7 @@ inputs:
     description: 'Rust toolchain name to use, e.g. `stable`, `nightly` or `1.68.0`. It will be installed if necessary and used regardless of local overrides and the `rust-toolchain.toml` file. However, if the input is set to `manual`, the action assumes some Rust toolchain is already installed and uses the default one.'
     default: 'stable'
   rust-target:
-    description: ''
+    description: 'Rust target to build for, e.g. `x86_64-pc-windows-msvc` or `aarch64-apple-darwin`. It will be installed if necessary and used regardless of the `.cargo/config.toml` file. However, if `rust-toolchain` is set to `manual`, the action assumes the target is already installed.'
     default: ''
   shared-key:
     description: 'A cache key that will be used instead of the automatic key based on the name of the GitHub job and values of the inputs `package`, `exclude` and `manifest-path`. Might be provided e.g. to share the cache between the jobs.'