Fix scaleway doc

[iaamp]

This updates only the documentation (no code change) of the DNS plugin for Scaleway.

Seemingly there was a change in the API of Scaleway, and while it seems to previously have used an API Token, now it needs the Secret Key of an API Key.

We don't have to change the code here, as it works if just passing the SCW_SECRET_KEY as the existing argument. This is likely ideal, to not break anyones scripted setups.

[github-actions]

Welcome
First thing: don't send PR to the master branch, please send to the dev branch instead.
Please make sure you've read our DNS API Dev Guide and DNS-API-Test.
Then reply on this message, otherwise, your code will not be reviewed or merged.
Please also make sure to add/update the usage here: https://github.com/acmesh-official/acme.sh/wiki/dnsapi2
We look forward to reviewing your Pull request shortly ✨
注意: 必须通过了 DNS-API-Test 才会被 review. 无论是修改, 还是新加的 dns api, 都必须确保通过这个测试.

[iaamp]

I have read the guide. This PR does not change any code - only adds to the documentation.

[Neilpang]

Any changes to the hook must be verified by the test.
Even if your chanage is only for doc, I would recommend you to finish the test. This is a good way to make sure the hook is still working by now.
Thank