Updated README.md file.

**Description**

@auraz Please don't forget to update documentation, if the changes you introduce in [one of your pull requests](https://github.com/innovecs-opensource/bustime/pull/6) require it. Just a friendly reminder = )

I changed the git clone URL to `https` since this way users who are not members of the [bustime](https://github.com/innovecs-opensource/bustime) can also clone this repository.

**Reviewers**

- @auraz