[examples] Update README.md - adaptive grid

test/examples/2pinfiltration/README.md

 This tutorial was copied from tests/porousmediumflow/2p/adaptive and restricted to the cell-centered finite volume TPFA discretization scheme.
-You need ALUGrid[0] in order to compile and run it.
+You need [ALUGrid][0] in order to compile and run it.
 
 # Two-phase flow with infiltration and adaptive grid
 
@@ -11,7 +11,51 @@ Soil contamination problem where DNAPL infiltrates a fully water saturated mediu
 
 ## Infiltration (point source)
 
+
+
 ## Adaptive grid
+### main.cc
+The following headers need to be included in the main file:
+
+```C++
+#include <dumux/adaptive/adapt.hh>
+#include <dumux/adaptive/markelements.hh>
+#include <dumux/adaptive/initializationindicator.hh>
+#include <dumux/porousmediumflow/2p/griddatatransfer.hh>
+#include <dumux/porousmediumflow/2p/gridadaptindicator.hh>
+```
+
+The grid adaptation is prepared during the initialization by the following steps:
+* instantiate indicator & data transfer, read parameters for indicator (ll. 111-115)
+* do initial refinement around sources/BCs (l. 118)
+* refine up to the maximum level (ll. 121-137)
+* do refinement for the initial conditions using the indicator (ll. 140-144)
+* update grid data after adaption (ll. 147-152)
+
+The indicator ... 
+
+During the time loop, the refinement indicator is computed (l. 191) and the respective elements to be refined are marked (ll. 194-196).
+
+In case of grid adaptation, the following updates are necessary (ll. 201-205):
+```C++
+ xOld = x; //!< Overwrite the old solution with the new (resized & interpolated) one
+ ssembler->setJacobianPattern(); //!< Tell the assembler to resize the matrix and set pattern
+ assembler->setResidualSize(); //!< Tell the assembler to resize the residual
+ gridVariables->updateAfterGridAdaption(x); //!< Initialize the secondary variables to the new (and "new old") solution
+ problem->computePointSourceMap(); //!< Update the point source map
+```
+
+### problem.hh
+...
+
+### params.input
+The following parameters in the `[Adaptive]` parameter group determine the grid adaptation behavior:
+* `RefineAtDirichletBC`: ...
+* `RefineAtFluxBC`: ...
+* `MinLevel`: ...
+* `MaxLevel`: ...
+* `CoarsenTolerance`: ...
+* `RefineTolerance`: ...