AIP-193: (Unactionable) error message shown after clicking link from advice on writing good error messages

[hugovk]

Steps to reproduce

1. Go to https://google.aip.dev/193
2. Scroll down to "Error messages" section:

Error messages

For each error, the service must populate the message field on google.rpc.Status. This error message,

• is a developer-facing, human-readable "debug message"
• is presented in the service's native language
• both explains the error and offers an actionable resolution to it (citation)

3. Click "citation"

Expected result

Either:

• The citation is shown
• A useful, actionable error message is shown

Actual result

A blank page is shown that only says "Service Unavailable"