[Jobs] [Doc] Add note about trailing slash for REST API

[architkulkarni]

It's a common mistake to forget the trailing slash in the URL for the REST API request, and the resulting error is not clear. This PR adds a brief reminder in the docs about the slash.

Why are these changes needed?

Related issue number

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[angelinalg]

We typically avoid using exclamation marks in technical documentation, but it sounds like we really want to warn users of this common trap. Plus it's in the code.