[doc][test] add 'args' to usage and add integration test

.github/main.workflow

@@ -0,0 +1,9 @@
+workflow "Integration tests" {
+  on = "push"
+  resolves = ["Quickstart"]
+}
+
+action "Quickstart" {
+  uses = "icepuma/rust-action@master"
+  args = "cd integration-test && cargo fmt -- --check && cargo clippy -- -Dwarnings && cargo test"
+}

.gitignore

@@ -1,2 +1,5 @@
 /.idea
 *.iml
+
+**/target
+**/*.rs.bk

README.md

@@ -19,5 +19,6 @@ workflow "Quickstart" {
 
 action "Quickstart" {
   uses = "icepuma/rust-github-action@master"
+  args = "cargo fmt -- --check && cargo clippy -- -Dwarnings && cargo test"
 }
 ```

integration-test/Cargo.lock

@@ -0,0 +1,4 @@
+[[package]]
+name = "rust-action"
+version = "0.1.0"
+

integration-test/Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "rust-action"
+version = "0.1.0"
+authors = ["Stefan Ruzitschka <icepuma@godda.mn>"]
+edition = "2018"
+
+[dependencies]

integration-test/src/lib.rs

@@ -0,0 +1,7 @@
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn it_works() {
+        assert_eq!(2 + 2, 4);
+    }
+}