docs: document the perf benefits of symlink startup options on Windows

docs/sphinx/pypi-dependencies.md

@@ -27,6 +27,18 @@ use_repo(pip, "my_deps")
 For more documentation, including how the rules can update/create a requirements
 file, see the bzlmod examples under the {gh-path}`examples` folder.
 
+We are using a host-platform compatible toolchain by default to setup pip dependencies.
+During the setup phase, we create some symlinks, which may be inefficient on Windows
+by default. In that case use the following `.bazelrc` options to improve performance if
+you have admin privileges:
+```
+startup --windows_enable_symlinks
+```
+
+This will enable symlinks on Windows and help with bootstrap performance of setting up the 
+hermetic host python interpreter on this platform. Linux and OSX users should see no
+difference.
+
 ### Using a WORKSPACE file
 
 To add pip dependencies to your `WORKSPACE`, load the `pip_parse` function and

python/private/toolchains_repo.bzl

@@ -262,8 +262,10 @@ exports_files(["python"], visibility = ["//visibility:public"])
         ]:
             continue
 
-        # Use the symlink command as it will create copies if the symlinks are not
-        # supported, let's hope it handles directories, otherwise we'll have to do this in a very inefficient way.
+        # symlink works on all platforms that bazel supports, so it should work on
+        # UNIX and Windows with and without symlink support. For better performance
+        # users should enable the symlink startup option, however that requires admin
+        # privileges.
         rctx.symlink(p, p.basename)
 
     is_windows = (os_name == WINDOWS_NAME)