Update swagger-cli migration guide

[lornajane]

We received some feedback about the swagger cli migration guide https://redocly.com/docs/cli/guides/migrate-from-swagger-cli/

• The -r must be replaced by -d

• Its "rules" and not "rule"

[Franqsanz]

Hello @lornajane, in which file is it located to be able to modify it?

[lornajane]

It's here https://github.com/Redocly/redocly-cli/blob/main/docs/guides/migrate-from-swagger-cli.md

Please test the commands as you add or change them in the docs.

[tatomyr]

Partially fixed by #1366.