Cover --python <dir> in "Using arbitrary Python environments" (#6457)

Closes https://github.com/astral-sh/uv/issues/6237

docs/pip/environments.md

@@ -97,10 +97,10 @@ regardless of where uv is installed. Note that if `VIRTUAL_ENV` is set to a dire
 **not** a [PEP 405 compliant](https://peps.python.org/pep-0405/#specification) virtual environment,
 it will be ignored.
 
-uv can also install into arbitrary, even non-virtual environments, with the `--python` argument
-provided to `uv pip sync` or `uv pip install`. For example,
-`uv pip install --python /path/to/python` will install into the environment linked to the
-`/path/to/python` interpreter.
+uv can also install into arbitrary, even non-virtual environments, with the `--python` option. For
+example, `uv pip install --python /path/to/python` will install into the environment linked to the
+`/path/to/python` interpreter regardless of whether or not it is a virtual environment. The
+`--python` option also accepts a path to the root directory of a virtual environment.
 
 For convenience, `uv pip install --system` will install into the system Python environment. Using
 `--system` is roughly equivalent to `uv pip install --python $(which python)`, but note that