Adds git install to readme "How To" and provides install URLs for all prerequisites

[TheAdamizer]

What is this change

Just a simple improvement to the Readme that mentions Git as a prerequisite. I added installation URLs for Platformio and VSCode as well, just to try and make things as explicit as possible for people who might be new to any of this.

Details

Platformio does mention git being needed in their quick start instructions, however it seems like this might be easy to miss as we just had a user get stuck building the project as they didn't know they needed it.

Changes

• Adds Git to the list of required prerequisites in the "How To" section of the readme.
• Adds markdown links for all of the prerequisites listed in the "How To" section.

[ecoreng]

Can you call out that GIT is required specifically pls?

[TheAdamizer]

Looks like this Fixes: #36