Add section on experimental features to Readme

README.md

@@ -165,6 +165,15 @@ These instructions are suitable for a clean **Ubuntu** or **Mac OS X** setup. Th
 
     **Installing DUNE and DORiE via `make install` into your usual work environment is strongly discouraged!**
 
+### Experimental Features
+The local operator implementing Richards equation's discretization supports
+multiple scheme settings. Setting these via the config file is disabled by
+default. You can enable this feature by reconfiguring DORiE with the CMake flag
+`-DEXPERIMENTAL_DG_FEATURES=On`, and rebuilding it.
+
+The configuration settings in the section `[dg.experimental]` will then override
+the default settings.
+
 
 ## Recommended Third-Party Software