JudgeServer API doc page lost

[alexwenbj]

Describe the bug
The link to JudgeServer API doc page lost.

To Reproduce
Steps to reproduce the behavior:

1. Go to '...'
2. Show 404 page

Expected behavior
Should show the help page.

Screenshots
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System (please complete the following information):

• OS: [e.g. iOS]
• Browser [e.g. chrome, safari]
• Version [e.g. 22]

Additional context
Add any other context about the problem here.