Update README

[kjugi]

Must add something descriptive to README file b/c, for now, we only have the name of our module. The points which should contain our README file:

• About what is this module and why we are creating it
• What advantages we gain from using this module
• Support table to browsers
• How to install our module by composer and by yarn. Give lines of code.
• What we need to working vue-checkout and what we need to know about the module
• How people can contribute to our module
• Info about License