add check for MappingType on sonata_type_admin FieldType
Remove installation instructions from tutorial

The documentation is not up to date, and it's mostly duplicated content
with the installation reference that is easily visible
Merge pull request #312 from marekkalnik/doc/tutorial/remove-installation-instructions

Remove installation instructions from tutorial
Merge pull request #311 from koyaan/master

add check for MappingType on sonata_type_admin FieldType
Merge branch 'sonata/master'