Markdown linting, fix link fragment, and update writeEvent function

[AndyVoutour]

1. Corrects the syntax in the operator docs for the writeEvent function in reconciler.ts .
2. Linted markdown
3. Updated the link fragment to reference demo section instead of non-existent build and deploy section.

The first issue can be easily confirmed by following the instructions in the operator docs - copying and pasting the reconciler.ts into an IDE will highlight the error.