feat(example-section): allow for markdown section underneath example card

[mesqueeb]

allow for extra description underneath the example

Example of source file:

bottom markdown content is to be displayed underneath example card here:
https://github.com/cycraft/planetar/blob/production/packages/example-card/src/components/ExampleSection.vue#L9

Will require manual parsing of file contents, as the top "description" part is retrieved via vue-docgen.

• use importHelpers raw loader to parse the file
• then use regex? to retrieve the bottom JSDoc comment section