We decided that `*.rules` is a more fitting (and concise) file extension
than `*.codexpolicy`, so we are changing the file extension for the
"execpolicy" effort. We are also changing the subfolder of `$CODEX_HOME`
from `policy` to `rules` to match.
This PR updates the in-repo docs and we will update the public docs once
the next CLI release goes out.
Locally, I created `~/.codex/rules/default.rules` with the following
contents:
```
prefix_rule(pattern=["gh", "pr", "view"])
```
And then I asked Codex to run:
```
gh pr view 7888 --json title,body,comments
```
and it was able to!
e0d7ac51d3