Add bundled read-only docs

tests/docs_tests.rs

@@ -0,0 +1,20 @@
+use tempfile::tempdir;
+
+#[test]
+fn install_extracts_bundled_docs_with_stamp() {
+    let root = tempdir().unwrap();
+
+    let docs_dir = cassady::docs::install(root.path()).unwrap();
+
+    assert_eq!(docs_dir, root.path().join("docs"));
+    assert!(docs_dir.join("README.md").is_file());
+    assert_eq!(
+        std::fs::read_to_string(docs_dir.join(".cass-docs-hash"))
+            .unwrap()
+            .trim(),
+        cassady::docs::docs_hash()
+    );
+
+    let second_install = cassady::docs::install(root.path()).unwrap();
+    assert_eq!(second_install, docs_dir);
+}