[enhancement/suggestion] - "how to add more pages" section in README

[pavanpej]

Hello @renyuanz,

Great job!
This Gatsby started was so good (simple and elegant enough) that I have decided to use this as a base for building my own personal site (with possibly a few customisations).
However, I thought it would be a good idea to also include a section in the README for this starter to add more pages to this (such as a contact or about or projects page) so that this could potentially also be used as a personal website.

[renyuanz]

Absolutely! Thanks for the suggestion.