Update proxy and uninstall sections at chrome/no-carga-[...]

- Add steps to the proxy section for Windows 10 and Linux.
- Add warning to suggest syncing Chrome before uninstalling Chrome and
  deleting all its data.
- Add pymdownx.tabbed and pymdownx.superfences MD extensions.

Change-Id: Icd2071d645360bf9924ab912506f317f27b6e1f6
diff --git a/mkdocs.yml b/mkdocs.yml
index 7136622..313af5f 100644
--- a/mkdocs.yml
+++ b/mkdocs.yml
@@ -19,6 +19,8 @@
   - markdown.extensions.footnotes
   - markdown.extensions.toc:
       permalink: true
+  - pymdownx.tabbed
+  - pymdownx.superfences
 nav:
   - 'Sobre esta web': 'index.md'
   - 'Chrome':