docs: add docs for functionObject tutorial

Author: FoamScience

tutorials/functionObject/README.md

@@ -0,0 +1,15 @@
+## Computing the SVD of OpenFOAM fields
+
+Running `openfoam-svd.py` will perform an SVD on OpenFOAM fields that results off
+of a `pitzDaily` case. The case runs with `simpleFoam` and communicates its fields
+to the `smartRedis` database through a `fieldsToSmartRedis` function object.
+
+## Usage of the Function Object with SmartSim ensembles
+
+The same function object is used in an ensemble setting to showcase a dummy parameter
+variation. The only requirement is that the solver has access to an environment variable:
+```bash
+export SSKEYIN=${SSKEYOUT}
+```
+This ensures each ensemble member reads and writes fields to a prefixed datasets to prevent
+race conditions and  members reading data from each other.