chore: Adds project structure details and next steps

[maxcell]

Summary

Here's a good start for us on what we could include for the project structure, how to make changes, and where folks could go next.

Definitely open to feedback on if it is too much or too little!

Relevant Issues

• Closes add dive deeper section to readme #1

[taty2010]

Should we also reference the "How to use this theme" page within the project? That page seems to have a good breakdown of what other tools can be used.
/how-to-use/

[tzmanics]

This is really fantastic, honestly when I wrote that issue i couldn't wrap my brain around how to structure this and this is great!

The only two things i would add are 1. Tatyana's suggestion of linking to the how to use page in the bottom section and 2. a section on how to change the homepage via src/pages/index.js, just like the great header and footer sections and maybe a specific nod to part of it like the hero component

        {/* Hero Container */}
        <Hero 
          maxWidth={'500px'}
          image={'/banner1.png'} 
          title={'Essentials for a cold winter'} 
          subtitle={'Discover Autumn Winter 2021'}
          ctaText={'shop now'}
          ctaAction={goToShop}
        />

gatsby-ecommerce-theme/src/pages/index.js

Line 31 in d7e37ba

{/* Hero Container */}

Other than that i'd say ship this gem!

[tzmanics]

[taty2010]

Looks Great!!