f0cec015b59ab484e81ca675d1170af5eb553911 Add small clarification to docs (thunderbiscuit)
Pull request description:
### Description
Very small fixes to documentation:
1. I got a DM last week from a user who thought we had a bug with our timestamps. It turns out he was using the milliseconds version of the Unix timestamp in his project and didn't realize we were giving out a standard Unix timestamp. The docs now mention this explicitly.
2. I noticed some small inconsistencies in the documentation on the public templates while porting them over to Kotlin. This PR also fixes that so that all templates use a common documentation wording.
### Checklists
#### All Submissions:
* [x] I've signed all my commits
* [x] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk/blob/master/CONTRIBUTING.md)
* [x] I ran `cargo fmt` and `cargo clippy` before committing
ACKs for top commit:
notmandatory:
Re-ACK f0cec015b59ab484e81ca675d1170af5eb553911
Tree-SHA512: ad42278126a0613fb1ba15f4e0ca92e05038389ac2e6b1015ea045f30ee8e92a40d6c089c35d0492bba0dc6d71e44b29879bd37a8bc491ff6367a89cab958db2
35bbe2beef