doc: add loginwithEmailandPassword, then redirect the user back to homepage

src/Auth/Login.js

@@ -10,6 +10,12 @@ function Login() {
 
   const signIn = (e) => {
     e.preventDefault();
+    auth
+      .signInWithEmailAndPassword(email, password)
+      .then((auth) => {
+        history.push("/");
+      })
+      .catch((error) => alert(error.message));
   };
 
   const register = (e) => {