We need better information about one-time keys.

**Link to problem area**:
https://spec.matrix.org/unstable/client-server-api/#key-algorithms

**Issue**
We should have a section about one-time keys that talks about how to generate them, how to upload, etc. We have a section about how to claim them, but not much else.

Read the key algorithms section at https://spec.matrix.org/unstable/client-server-api/#key-algorithms and the existing one-time-key claiming documentation. Identify the established terminology and protocol requirements, then add coverage for generating and uploading one-time keys; done means those workflows are documented alongside claiming.

Written by the indexing model from the issue text.