docs(standard): add more context to softwareType definitions

Co-authored-by: Tom Ootes <tom@ootes.io>

Author: libremente

docs/standard/schema.core.rst

@@ -274,20 +274,22 @@ Key ``softwareType``
 
 The keys are:
 
--  ``standalone/mobile`` - The software is a standalone, self-contained
-   The software is a native mobile app.
+-  ``standalone/mobile`` - The software is a standalone application, typically
+  installed and run on a mobile operating system.
 -  ``standalone/iot`` - The software is suitable for an IoT context.
 -  ``standalone/desktop`` - The software is typically installed and run in a  
    a desktop operating system environment.
--  ``standalone/web`` - The software represents a web application usable by
-   means of a browser. 
--  ``standalone/backend`` - The software is a backend application.
--  ``standalone/other`` - The software has a different nature from the once
+-  ``standalone/web`` - The software is a web application that runs on a server
+  and is accessible through a web browser.
+-  ``standalone/backend`` - The software is a backend application that provides
+  interfaces (e.g., APIs) for other services. Typically it does not provide
+  direct user interfaces.
+-  ``standalone/other`` - The software has a different nature from the ones 
    listed above.  
 -  ``addon`` - The software is an addon, such as a plugin or a
    theme, for a more complex software (e.g. a CMS or an office suite).
--  ``library`` - The software contains a library or an SDK to make it
-   easier to third party developers to create new products.
+-  ``library`` - The software is a library or SDK intended to be used 
+   by developers in other software projects. 
 -  ``configurationFiles`` - The software does not contain executable
    script but a set of configuration files. They may document how to
    obtain a certain deployment. They could be in the form of plain