Version pin mkdocs to avoid nasty surprises

fix use_directory_urls defaulting to false

docs/requirements-docs.txt

@@ -1,3 +1,4 @@
+mkdocs==1.2
 mkdocs-material==7.1.7
 mdx_truly_sane_lists==1.2
 pymdown-extensions==8.2

mkdocs.yml

@@ -1,5 +1,7 @@
 site_name: Freqtrade
+site_url: https://www.freqtrade.io/
 repo_url: https://github.com/freqtrade/freqtrade
+use_directory_urls: True
 nav:
     - Home: index.md
     - Quickstart with Docker: docker_quickstart.md