Update alert rendering to fix visual bug

[zachmargolis]

Changes proposed in this pull request:

There was a bug in the rendering of https://handbook.tts.gsa.gov/travel-and-leave/travel-guide-table-of-contents/

I spot-checked one more alertbox and it seems to be ok with link content still

before	after

Bonus Changes

Also updates README instructions for local development

security considerations

• Removing an extra layer of HTML processing should be safe?

[mgwalker]

The alert for the software warning one is broken now, but that's not surprising. That one and the travel guide make incompatible assumptions about the alert.

I'll argue that the software tools usage is correct and the render filter should be applied. The problem with the travel guide alert is that it is also rendering the content, so it's basically being run through the liquid parser twice, but the second pass uses the markdown-it renderer, which by default converts HTML to plaintext. By changing that configuration to preserve HTML, the render filter works as expected!

This was a really good find!

[zachmargolis]

Ah thanks for helping me dig one layer deeper!