links in importlib.metadata.rst replaced with sphinx references (GH-17730)

The importlib.metadata documentation uses hardcoded links to internal
pages. This results in minor rendering issues. This change replaces
the hardcoded links with suitable Sphinx roles.

Signed-off-by: Oleg Höfling <oleg.hoefling@gmail.com>
diff --git a/Doc/reference/import.rst b/Doc/reference/import.rst
index c958263..20a2ea6 100644
--- a/Doc/reference/import.rst
+++ b/Doc/reference/import.rst
@@ -202,6 +202,8 @@
 reinitialise the module contents by rerunning the module's code.
 
 
+.. _finders-and-loaders:
+
 Finders and loaders
 -------------------