Update eva2_methods.cpp
Update eva2_methods.cpp

Added a comment into the method that is responsible to read in the eva2 database information of the soil profile; the comment contains some advice regarding the conversion of the value that should be followed when the stone content of the soil profile is actively used; now the stone content is not read from the database and uncommented in the MONICA code
zalf-lsa/monica,zalf-lsa/monica,zalf-lsa/monica