Update user pays model docs to include info about resource usage and costs

[reynaldichernando]

once user understands what user pays is, they need to know what they "pay" for and how much
https://docs.puter.com/user-pays-model/

we need to add info to this page for

• costs of each APIs, broken down by specific actions
• and where they user can see what they "pay" which is just linking to either the dashboard or settings app
• also detail about how they are getting free credits to perform these user-pays action

[vanshika2408]

Hi! I’d like to work on this issue and submit a documentation update PR. Please let me know if that works.

[reynaldichernando]

hi @vanshika2408 , thanks for the interest, i'll handle this one for now
we still have other open issues if you want to contribute, or keep a look out for more!