docs: Clarify SuspendTemplate.duration.

[cjyar]

Fixes #TODO

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[cjyar]

In the online docs, the description implies the field should be an integer, even though the type is string. This PR tries to fix that by making the description clearer. The new description was copied from here.

[caelan-io]

LGTM. Thanks for all the additional clarification throughout.