doc: improve alias error msg in pip hubs (#2458)

Summary:
* Add more flag values that we actually use.
* Point users to online docs.

I still think it is not good enough when somebody needs to debug, but I
am not sure what to add. Maybe we just need user documentation outlining
what each config setting means and what values it is using? Maybe we
should generate the config settings inside the `rules_python` repository
so that we have better visibility into what needs to be documented and
explained.

python/private/pypi/pkg_aliases.bzl

@@ -36,22 +36,31 @@ load(":whl_target_platforms.bzl", "whl_target_platforms")
 # it. It is more of an internal consistency check.
 _VERSION_NONE = (0, 0)
 
+_CONFIG_SETTINGS_PKG = str(Label("//python/config_settings:BUILD.bazel")).partition(":")[0]
+
 _NO_MATCH_ERROR_TEMPLATE = """\
 No matching wheel for current configuration's Python version.
 
 The current build configuration's Python version doesn't match any of the Python
-wheels available for this wheel. This wheel supports the following Python
+wheels available for this distribution. This distribution supports the following Python
 configuration settings:
     {config_settings}
 
 To determine the current configuration's Python version, run:
     `bazel config <config id>` (shown further below)
-and look for
-    {rules_python}//python/config_settings:python_version
 
-If the value is missing, then the "default" Python version is being used,
-which has a "null" version value and will not match version constraints.
-"""
+and look for one of:
+    {settings_pkg}:python_version
+    {settings_pkg}:pip_whl
+    {settings_pkg}:pip_whl_glibc_version
+    {settings_pkg}:pip_whl_muslc_version
+    {settings_pkg}:pip_whl_osx_arch
+    {settings_pkg}:pip_whl_osx_version
+    {settings_pkg}:py_freethreaded
+    {settings_pkg}:py_linux_libc
+
+If the value is missing, then the default value is being used, see documentation:
+{docs_url}/python/config_settings"""
 
 def _no_match_error(actual):
     if type(actual) != type({}):
@@ -68,7 +77,8 @@ def _no_match_error(actual):
                 for value in (key if type(key) == "tuple" else [key])
             ])),
         ).lstrip(),
-        rules_python = "rules_python",
+        settings_pkg = _CONFIG_SETTINGS_PKG,
+        docs_url = "https://rules-python.readthedocs.io/en/latest/api/rules_python",
     )
 
 def pkg_aliases(