Add devcontainer.json reference

[bamurtaugh]

Adding the devcontainer.json reference content so that it is available in this repo. Using a docs folder to contain this and any potential future docs we'd like to include.

cc @chrmarti @joshspicer @edgonmsft

[joshspicer]

Great to see this here 🎉

[Chuxel]

I think there's probably some tweaking we should make to make the reference a bit less VS Code specific. Some thoughts.

[bamurtaugh]

@Chuxel @chrmarti I updated the folder structure to:

/docs
-- /images
-- /specs
---- devcontainerjson-reference.md
---- supporting-tools.md
---- /schemas

Let me know if that seems reasonable to you.

[Chuxel]

Couple other thoughts

[bamurtaugh]

Hey team, do we think this is ready to merge? And we can always continue revising in the future?

[Chuxel]

@bamurtaugh Yes with one possible caveat...

@chrmarti Is the customizations.vscode update in the version of everything that just shipped?

I'm kind of thinking we should update this reference to call out what the customizations property is for under the "tool specific properties" section in the main reference, and then update the tool specific properties to reflect this change.

[chrmarti]

I have only added the customizations wildcard for now. customizations.vscode is not there yet.

[bamurtaugh]

I can hold off on merging until customizations.vscode is in, and then update this PR accordingly.

[bamurtaugh]

Closing in favor of #33.