Add formatting instructions

[jackrein]

The README did not mention the extension supports formatting of .smithy files. This change advertises the formatting feature and adds instructions for use

Tested auto formatting in VS code by adding and removing the block in settings.json and attempting to format via the command palette. Formatting worked when the block was there, and did not do anything when the block was omitted.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[yasmewad]

Can you provider information on how did you test it?

Thanks!

[jackrein]

Hey @yasmewad, I added my ad-hoc testing method to the description above

Tested auto formatting in VS code by adding and removing the block in settings.json and attempting to format via the command palette. Formatting worked when the block was there, and did not do anything when the block was omitted.

[milesziemer]

Formatting should work without this setting, it should be automatically wired up because the language server provides it (anecdotally, I don't have it in my vscode settings, and both format on save and the Format Document command work). It may have been fixed in a newer version of the extension. Closing this for now - if you update to the latest version of the extension and still need the setting, please open an issue, as it should work without any configuration.