fix typo intro_to_filesystems.md

mkdocs/docs/intro_to_filesystems.md

@@ -6,7 +6,7 @@ mergerfs is a union filesystem that manages other filesystems. To
 understand how mergerfs works and what the features do and mean you
 must understand at least the basics of how filesystems work. Much of
 the confusion with mergerfs is based in a lack of knowledge about
-filesystems. This section of the documentation is provide a primer for
+filesystems. This section of the documentation provides a primer for
 those needing that knowledge.