feat: add default command-not-found handler

src/commands/default.ts

@@ -0,0 +1,18 @@
+const createDefault = (): string[] => {
+  const defaultMsgArr = [
+    "<br>",
+    "COMMAND NOT FOUND",
+    "Type <span class='command'>'help'</span> to get started.",
+    "<br>",
+  ];
+
+  const defaultMsg: string[] = [];
+
+  defaultMsgArr.forEach((ele) => {
+    defaultMsg.push(ele);
+  });
+
+  return defaultMsg;
+};
+
+export const DEFAULT = createDefault();