DOC: Create a new chapter with extended filenames and environment variables in cookbook. Document all environment variables

add in TOC the file
update the introduction
add the reference about the section

Extended filemame are described in the OTB-Application section which is not the right place I think
No examples are provided,I have added two : one for reader and another for writer
I have added also a link about create_option of GDAL for GeoTIFF