Add symlink command documentation and comprehensive error testing

Co-authored-by: imjasonh <210737+imjasonh@users.noreply.github.com>

README.md

@@ -127,6 +127,7 @@ Test scripts use the [`txtar`](https://pkg.go.dev/github.com/rogpeppe/go-interna
 - **mv** - Move/rename files
 - **rm** - Remove files/directories
 - **chmod** - Change file permissions
+- **symlink** - Create symbolic links
 - **env** - Set environment variables
 - **cmpenv** - Compare files with environment variable substitution
 - **stdin** - Set stdin for next command

tests/builtin_commands.rs

@@ -206,3 +206,19 @@ original content"#;
     let result = run_test(&script_path);
     assert!(result.is_ok(), "Symlink test failed: {:?}", result);
 }
+
+#[test] 
+fn test_symlink_error_cases() {
+    let temp_dir = TempDir::new().unwrap();
+    let script_path = temp_dir.path().join("symlink_error_test.txt");
+
+    let script_content = r#"# Test symlink error cases
+! symlink
+! symlink only_one_arg
+! symlink too many arguments here"#;
+
+    fs::write(&script_path, script_content).unwrap();
+
+    let result = run_test(&script_path);
+    assert!(result.is_ok(), "Symlink error test failed: {:?}", result);
+}