Add Polish language to docs

* tested locally... this should work

Author: sspencerwire

mkdocs.yml

@@ -65,6 +65,7 @@ plugins:
           ja: 日本語
           zh: 简体中文
           sv: Svenska
+          pl: Polish
           pt: Português
           ru: Russian
   - git-revision-date-localized:
@@ -97,6 +98,9 @@ extra:
     - name: 日本語
       link: ./ja/
       lang: ja
+    - name: Polish
+      link: ./pl/
+      lang: pl
     - name: Português
       link: ./pt/
       lang: pt