refactor(docs): add markdown-del-ins extension for strike through text

mkdocs.yml

@@ -47,6 +47,7 @@ markdown_extensions:
   - admonition
   - codehilite:
       linenums: true
+  - markdown_del_ins
   - toc:
       permalink: True
   - footnotes

requirements.txt

@@ -5,3 +5,4 @@ plantuml~=0.2
 plantuml-markdown~=3.1
 pymdown-extensions~=6.2
 certifi~=2019.9
+markdown_del_ins~=1.0