fixed some grammar (#945)

Co-authored-by: eric <ericgoto0212@gmail.com>

README.rst

@@ -34,7 +34,7 @@ Quickly add security features to your Flask application.
 
 Notes on this repo
 ------------------
-This is a independently maintained version of Flask-Security forked from the 3.0.0
+This is an independently maintained version of Flask-Security forked from the 3.0.0
 version of the `Original <https://github.com/mattupstate/flask-security>`_
 
 Goals

flask_security/utils.py

@@ -140,7 +140,7 @@ def find_csrf_field_name():
 
 def is_user_authenticated(user: User | None) -> bool:
     """
-    return True is user is authenticated.
+    return True if user is authenticated.
 
     With Flask-Login <=0.6.x and Flask-Security <5.4 current_user was always
     set - for non-authenticated users it pointed to an AnonymousUser