docs: add mkdocs-print-site-plugin (#37)

* Add mkdocs-print-site-plugin to requirements

* Add 'print-site' to the `plugins:`

Author: kozo2

docs/requirements.txt

@@ -1,3 +1,4 @@
 mkdocstrings
 mkdocstrings-python
 mkdocs-material
+mkdocs-print-site-plugin

mkdocs.yml

@@ -25,6 +25,7 @@ plugins:
             show_labels: true
             show_symbol_type_heading: true
             show_symbol_type_toc: true
+  - print-site
 
 markdown_extensions:
   - admonition