• https://vscode-ext-docs.azurewebsites.net/api/language-extensions/snippet-guide
• https://github.com/Microsoft/vscode-extension-samples/tree/master/snippet-sample

The source of doc is at https://github.com/Microsoft/vscode-docs/blob/ext-docs/api/language-extensions/snippet-guide.md

Please review this guide / sample combo. Edit as you fit, and add things you think are missing.