Updates the configuration documentation to clarify and improve the
description of the `developer_instructions` and `instructions` fields.
Documentation updates:
* Added a description for the `developer_instructions` field in
`docs/config.md`, clarifying that it provides additional developer
instructions.
* Updated the comments in `docs/example-config.md` to specify that
`developer_instructions` is injected before `AGENTS.md`, and clarified
that the `instructions` field is ignored and that `AGENTS.md` is
preferred.
___
ref #7973
Thanks to @miraclebakelaser for the message. I have double-confirmed
that developer instructions are always injected before user
instructions. According to the source code
[codex_core::codex::Session::build_initial_context](https://github.com/openai/codex/blob/rust-v0.77.0-alpha.2/codex-rs/core/src/codex.rs#L1279),
we can see the specific order of these instructions.
372de6d2c5