doc: Add empty migration page

doc/index.rst

@@ -16,6 +16,7 @@ Welcome to the official polybar documentation.
    user/ipc
    user/modules/index
    user/default-config
+   migration/index
 
 .. toctree::
    :maxdepth: 1

doc/migration/3.7/index.rst

@@ -0,0 +1,2 @@
+Migrating From Version 3.6 to 3.7
+=================================

doc/migration/index.rst

@@ -0,0 +1,19 @@
+Polybar Migration Guides
+========================
+
+Updating polybar to the newest version often requires updating your
+configuration files to use the newest features and replace outdated settings.
+
+Starting from version 3.7, we include a small guide here for how to migrate
+from the previous version.
+If you are upgrading over multiple versions (e.g. from 3.5 to 3.7), also read
+the migration guides for all versions in between.
+
+For migration guides before version 3.7, please look at our `release blog posts
+<https://polybar.github.io/blog/>`_.
+
+.. toctree::
+   :maxdepth: 1
+   :caption: Guides
+
+   3.7/index