Remove uv pip sync suggestion with pyproject.toml (#14510)

## Summary

I think doing this would almost always be a mistake, since it won't
install any transitive dependencies. Instead, I took the opportunity to
mention the `pylock.toml` format.

Closes
#14507 (comment).

Author: charliermarsh

docs/pip/compile.md

@@ -127,10 +127,10 @@ To sync an environment with a `requirements.txt` file:
 $ uv pip sync requirements.txt
 ```
 
-To sync an environment with a `pyproject.toml` file:
+To sync an environment with a [PEP 751](https://peps.python.org/pep-0751/) `pylock.toml` file:
 
 ```console
-$ uv pip sync pyproject.toml
+$ uv pip sync pylock.toml
 ```
 
 ## Adding constraints