Update setup.py meta and README with constraint [ci skip]

README.rst

@@ -41,8 +41,7 @@ Quickstart
 
 Cachalot officially supports Python 3.6-3.9 and Django 2.2 and 3.0-3.2 with the databases PostgreSQL, SQLite, and MySQL.
 
-No upper limit is imposed by cachalot. However, if you use a Django version that is not officially supported,
-you may end up battling mounting errors/exceptions and cache misses. Please stay within compatibility.
+Note: an upper limit on Django version is set for your safety. Please do not ignore it.
 
 Usage
 -----

setup.py

@@ -17,22 +17,19 @@
     author='Bertrand Bordage, Andrew Chen Wang',
     author_email='acwangpython@gmail.com',
     url='https://github.com/noripyt/django-cachalot',
-    description='Caches your Django ORM queries '
-                'and automatically invalidates them.',
+    description='Caches your Django ORM queries and automatically invalidates them.',
     long_description=open('README.rst').read(),
     classifiers=[
         'Development Status :: 5 - Production/Stable',
         'Framework :: Django',
         'Intended Audience :: Developers',
         'License :: OSI Approved :: BSD License',
         'Operating System :: OS Independent',
-        'Framework :: Django :: 2.0',
-        'Framework :: Django :: 2.1',
         'Framework :: Django :: 2.2',
         'Framework :: Django :: 3.0',
         'Framework :: Django :: 3.1',
+        'Framework :: Django :: 3.2',
         'Programming Language :: Python :: 3',
-        'Programming Language :: Python :: 3.5',
         'Programming Language :: Python :: 3.6',
         'Programming Language :: Python :: 3.7',
         'Programming Language :: Python :: 3.8',