docs: Link to pytest standard doctest plugin

Author: tony

README.md

@@ -76,7 +76,7 @@ $ python -m doctest_docutils README.md -v
 
 ### pytest plugin
 
-_This plugin disables pytest's standard `doctest` plugin._
+_This plugin disables [pytest's standard `doctest` plugin]._
 
 This plugin integrates with the above module.
 
@@ -89,6 +89,8 @@ Like the above module, it supports docutils' own `doctest_block` and a basic
 
 See more: <https://gp-libs.git-pull.com/doctest/pytest.html>
 
+[pytest's standard `doctest` plugin]: https://docs.pytest.org/en/stable/how-to/doctest.html#doctest
+
 ## sphinx plugins
 
 ### Plain-text issue linker (`linkify-issues`)

docs/doctest/pytest.md

@@ -5,7 +5,7 @@
 
 :::{note}
 
-This plugin disables pytest's standard `doctest` plugin.
+This plugin disables {ref}`pytest's standard doctest plugin <pytest:doctest>`.
 
 :::