Update README (about backward compatibility)

README.md

@@ -315,7 +315,7 @@ The standard Lua API is extended with the following features:
 * `get_key(table, value)` - returns the key of the table element;
 * `round(x, n)` - rounds the number;
 
-The kit also includes:
+AIO Launcher also includes:
 
 * `md_colors` - Material Design color table module (source is in this repository, [help](https://materialui.co/colors));
 * `url` - a module with functions for encoding / decoding a string in a URL from the Lua Penlight library;
@@ -340,6 +340,16 @@ In order for AIO Launcher to correctly display information about the script in t
 -- version = "1.0"
 ```
 
+# Backward compatibiliy
+
+AIO Launcher mantains backward compatibility with existing APIs. But if you want to use API functions which appeared later than 4.0.0 you'd better use a special meta tag which will hide your script on all previous versions of the application.
+
+For example, let's say you want to use the `weather` module that appeared in version 4.1.3. In this case, add the following line to the script's metadata:
+
+```
+-- aio_version = "4.1.3"
+```
+
 # Contribution
 
 If you want your scripts to be included in the repository and the official AIO Launcher kit - create a pull request or email me: zobnin@gmail.com. Also I am always ready to answer your questions and discuss extending the current API.