Create a Gatsby example project

[andrico1234]

BST is used with calisthenicsskills, which is built using Gatsby.

SInce gatsby compiles sites to static on the server, it's important to not reference any globals like navigator or window directly in code that gets compiled on the server. Instead any references need to be contained within a componentDidMount(), or useEffect(), so that the global gets referenced at runtime.

It's difficult testing this with a separate site, so having a gatsby example site on the repo for the sole purpose of testing running/compiling with the local version of BST would be incredibly useful.