Improve Getting Started

[stevezhang1999]

The tutorial is awesome! I found that the tutorial can be improved to be more beginner-friendly:

1. the version stated in the tutorial is no longer supported by Remix. I update the version in the instruction to the latest version - this is working as I tried.
2. The instruction mentions Sequencer when explaining what will happen when you call a function. This is the first time Sequencer appears in the book, so I think it would be super helpful if we briefly mention what it is and provide a link for more details.

[gianalarcon]

LGTM. Thank you for your contribution. You have to run prettier --write . to pass the linter.

[stevezhang1999]

LGTM. Thank you for your contribution. You have to run prettier --write . to pass the linter.

Thank you so much for reminding me this. Now it should pass the linter.