message: add a list of events emitted by viewer.js to README.md
diff: @@ -9,3 +9,32 @@ We provide additional features by setting up new event listeners in `latexworksh
  We can see the [changes](https://github.com/James-Yu/LaTeX-Workshop/commit/c015e2a4aeb56c18c3f8430b9bea63ab4db27b01#diff-ff661e0ff756ae1ff026c0e8f4561d0e) we have made to `viewer.js`. We had better find a way to achieve this without modifying `viewer.js`.
  JavaScript files, `latexworkshop.js`, and others, are generated in `../out/viewer/` from TypeScript files.
  +
  +### Events emitted by `viewer.js`
  +
  +When opening a PDF file. In order.
  +
  +1. webviewerloaded
  +2. DOMContentLoaded (not by `viewer.js`)
  +3. baseviewerinit
  +4. pagesinit
  +5. documentloaded
  +7. documentinit
  +8. PDF da551cb... [...] (PDF.js: 2.2.228) (a log message is output)
  +9. pagerendered
  +1. pagesloaded
  +1. textlayerrendered
  +1. pagerendered
  +1. textlayerrendered
  +
  +When reloading a PDF file. In order.
  +
  +1. pagesinit
  +1. documentloaded
  +1. documentinit
  +1. PDF da551cb... [...] (PDF.js: 2.2.228) (a log message is output)
  +1. pagerendered
  +1. pagesloaded
  +1. textlayerrendered
  +1. pagerendered
  +1. textlayerrendered
  