Add 'Contributing' section to README.md
Add 'Contributing' section to README.md

InboxHealth/sweetalert2,johan-weitner/SweetAlert3,erbelair/sweetalert2,toadkicker/sweetalert2,birjolaxew/sweetalert2,massa1240/sweetalert2,toadkicker/sweetalert2,erbelair/sweetalert2,limonte/sweetalert2,birjolaxew/sweetalert2,InboxHealth/sweetalert2,massa1240/sweetalert2,johan-weitner/SweetAlert3