Update README.md

Merge pull request #165 from quintenbuis/master

Add Laravel 9 compatibility

Merge pull request #143 from bumbummen99/contributors-readme-action-M…

…-4_Tz-nNv

contributors readme action update

Merge pull request #115 from geisi/master

Fixing InvalidArgumentException when adding buyable models

Merge pull request #111 from Norris1z/master

Use current instance when checking if storedCartWithIdentifierExists

Merge pull request #113 from thefilip/macroable

Add macroable trait

Merge pull request #104 from manojo123/master

Add new events (adding, updating, removing)

Added Calculators to the Readme

Merge pull request #3 from bumbummen99/fix_cart_database_timestamps

Fix cart database timestamps

Merge pull request #70 from royduin/patch-1

Laravel 7.x support