Implement llms.txt for documentation site

[amerryma]

Feature description

I've been seeing this new strategy for LLMS to interact with documentation and thought Graphile Worker could implement this as well. Thoughts or concerns? Here is some more information on the standard: https://llmstxthub.com/about.

Motivating example

See the other folks that have this:

• https://supabase.com/llms.txt
• https://ai-sdk.dev/llms.txt
• [docs-infra] Add a script to generate Material UI llms.txt and docs markdown. mui/material-ui#46308
• https://docs.anthropic.com/llms.txt
• https://docs.perplexity.ai/llms.txt
• https://docs.zapier.com/llms.txt
• https://gitbook.com/docs/llms.txt

Breaking changes

None

Supporting development

I [tick all that apply]:

• am interested in building this feature myself
• am interested in collaborating on building this feature
• am willing to help testing this feature before it's released
• am willing to write a test-driven test suite for this feature (before it exists)
• am a Graphile sponsor ❤️
• have an active support or consultancy contract with Graphile