List differences from swipl source distribution. (#1172)

* List differences from swipl source distribution.

swipl/content.md

@@ -27,3 +27,22 @@ CMD ["swipl", "/app/start.pl"]
 ```
 
 This will extract and copy your source files to the image and then set the default command to run your application.
+
+## Differences from the SWI-Prolog source distribution
+
+### Excluded packages
+
+-	jpl - interop with Java is excluded, as Java isn't included on the image
+-	xpce - XPCE is excluded, as it's used only for the GUI platform
+
+### Included addins
+
+This image includes several SWI-Prolog addins that are commonly used, complex to build, and require little additional space.
+
+-	space
+-	prosqlite
+-	rocksdb\*
+-	hdt\*
+-	rserve_client
+
+\*excluded from ARM architecture images due to platform constraints