docs: add brief autoloading help page, fix smarty3 help page name

doc/Home.md

@@ -47,8 +47,10 @@ Friendica Documentation and Resources
 * [Theme Development](help/themes)
 * [Smarty 3 Templates](help/smarty3-templates)
 * [Database schema documantation](help/database)
+* [Class Autoloading](help/autoloader)
 * [Code - Reference(Doxygen generated - sets cookies)](doc/html/)
 
+
 **External Resources**
 
 * [Main Website](http://friendica.com)

doc/autoloader.md

@@ -0,0 +1,17 @@
+Autoloader
+==========
+
+* [Home](help)
+
+There is some initial support to class autoloading in Friendica core.
+
+The autoloader code is in `include/autoloader.php`.
+It's derived from composer autoloader code.
+
+Namespaces and Classes are mapped to folders and files in `library/`,
+and the map must be updated by hand, because we don't use composer yet.
+The mapping is defined by files in `include/autoloader/` folder.
+
+Currently, only HTMLPurifier library is loaded using autoloader.
+
+