Provide instructions in the ReadMe on how to install for the first time

[JavierCane]

We should modify the ☝️ Instructions readme section in order to provide clear instructions on how to procedure with a clean MacOS installation.

That is, right now we're suggesting to clone this repo, but this repo is intended to serve as your environment setup starting point even when you don't have the git command available to perform the git clone operation.

I would suggest to divide this ☝️ Instructions section on two different sub-sections:

• How to bootstrap your environment: Instructions on how to download via curl and executing the install scripts because you don't have git yet
• How to tweak your already configured environment: More or less the instructions already available in this section