markdownlint vendor demo

Demo for DavidAnson/vscode-markdownlint#38

1. Clone this repo
2. Open README.md in VSCode.
3. Press Ctrl+T (Go to Symbol in Workspace)

You should see a lot of hits from vendor:

Also, the problems panel will show lint results of library files:

All this with just README.md open.

node_modules are fine

Try the same as above, you should not be getting hits from node_modules, i.e., everything behaves correctly.