Add crowdin support for translations (#134)

* Move docs to its own folder

* Add crowdin configuration

antora-playbook.yml

@@ -5,7 +5,7 @@ site:
 content:
   sources:
     - url: https://github.com/decidim/documentation
-      start_path: en
+      start_path: docs/en
       branches:
         - release/0.27-stable
         - release/0.26-stable

crowdin.yml

@@ -0,0 +1,3 @@
+files:
+  - source: /docs/en/**/*.adoc
+    translation: /docs/%two_letters_code%/**/%original_file_name%