Add markdown output (#1503)

crates/nu-cli/tests/format_conversions/markdown.rs

@@ -0,0 +1,25 @@
+use nu_test_support::{nu, pipeline};
+
+#[test]
+fn out_md_simple() {
+    let actual = nu!(
+        cwd: ".", pipeline(
+        r#"
+            echo 3 | to-md
+        "#
+    ));
+
+    assert_eq!(actual, "3");
+}
+
+#[test]
+fn out_md_table() {
+    let actual = nu!(
+        cwd: ".", pipeline(
+        r#"
+            echo '{"name": "jason"}' | from-json | to-md
+        "#
+    ));
+
+    assert_eq!(actual, "|name||-||jason|");
+}