Fix some outdated documentation discussing Python environments (#6058)

Starting on https://github.com/astral-sh/uv/issues/5966 noticed various
problems

docs/concepts/python-versions.md

@@ -134,20 +134,6 @@ To exclude downloads and only show installed Python versions:
 $ uv python list --only-installed
 ```
 
-## Discovery of virtual environments
-
-Some uv commands may use a Python interpreter from a virtual environment. When searching for virtual
-environments, uv prioritizes (in order):
-
-- The `VIRTUAL_ENV` environment variable.
-- The `CONDA_PREFIX` environment variable.
-- A `.venv` directory in the working directory.
-- A `.venv` directory in any parent directory.
-
-After exhausting these possibilities, uv will either
-[search for a Python installation](#discovery-of-python-versions) or exit with an error if the
-command requires a virtual environment.
-
 ## Discovery of Python versions
 
 When searching for a Python version, the following locations are checked:
@@ -158,6 +144,12 @@ When searching for a Python version, the following locations are checked:
 - On Windows, the Python interpreter returned by `py --list-paths` that matches the requested
   version.
 
+In some cases, uv allows using a Python version from a virtual environment. In this case, the
+virtual environment's interpreter will be checked for compatibility with the request before
+searching for an installation as described above. See the
+[pip-compatible virtual environment discovery](../pip/environments.md#discovery-of-python-environments)
+documentation for details.
+
 When performing discovery, non-executable files will be ignored. Each discovered executable is
 queried for metadata to ensure it meets the [requested Python version](#requesting-a-version). If
 the query fails, the executable will be skipped. If the executable satisfies the request, it is used

docs/pip/environments.md

@@ -107,18 +107,9 @@ will search for a virtual environment in the following order:
 If no virtual environment is found, uv will prompt the user to create one in the current directory
 via `uv venv`.
 
-If the `--system` flag is included, uv will skip virtual environments and search for:
+If the `--system` flag is included, uv will skip virtual environments search for an installed Python
-
+version. Similarly, when running a command that does not mutate the environment such as
-- The Python interpreter available as `python3` on macOS and Linux, or `python.exe` on Windows.
+`uv pip compile`, uv does not _require_ a virtual environment — however, a Python interpreter is
-- On Windows, the Python interpreter returned by `py --list-paths` that matches the requested
+still required. See the documentation on
-  version.
+[Python discovery](../concepts/python-versions.md#discovery-order) for details on the discovery of
-
+installed Python versions.
-If a specific Python version is requested, e.g., `--python 3.7`, additional executable names are
-included:
-
-- The Python interpreter available as, e.g., `python3.7` on macOS and Linux.
-
-When running a command that does not mutate the environment such as `uv pip compile`, uv does not
-_require_ a virtual environment. Instead, it needs a Python toolchain to create ephemeral
-environments. See the documentation on
-[toolchain discovery](../concepts/python-versions.md#discovery-order) for details on discovery.