Update README

Author: dcvz

README.md

@@ -52,6 +52,7 @@ Afterward, the `components` and `target` specified via inputs are installed in a
 | `target`     | Additional target support to install e.g. `wasm32-unknown-unknown`                     |               |
 | `components` | Comma-separated string of additional components to install e.g. `clippy, rustfmt`      |               |
 | `cache`      | Automatically configure Rust cache (using `Swatinem/rust-cache`)                       | true          |
+| `matcher`    | Enable problem matcher to surface build messages and formatting issues                 | true          |
 | `rustflags`  | Set the value of `RUSTFLAGS` (set to empty string to avoid overwriting existing flags) | "-D warnings" |
 
 ### RUSTFLAGS