ENH: README.txt: description of directional cht

tutorials/heatTransfer/chtMultiRegionFoam/multiRegionLiquidHeater/README.txt

@@ -0,0 +1,16 @@
+To run with directional thermo:
+
+- compile chtMultiRegionFoam/solid/setRegionSolidFields.H with
+
+    tmp<volSymmTensorField> tkappa = thermo.directionalK();
+    const volSymmTensorField& kappa = tkappa();
+
+- change in e.g. heater:
+
+    - in constant/heater/solidThermophysicalProperties:
+
+        thermoType directionalKSolidThermo;
+
+    - in 0/heater/T:
+
+        K               directionalSolidThermo;