DOC: Clarify tofile requirement
DOC: Clarify tofile requirement

Clarify that tofile requires a file that can be directly written to
and not a general file-like object

madphysicist/numpy,endolith/numpy,shoyer/numpy,jakirkham/numpy,Eric89GXL/numpy,gfyoung/numpy,abalkin/numpy,MSeifert04/numpy,grlee77/numpy,pbrod/numpy,mattip/numpy,charris/numpy,mhvk/numpy,seberg/numpy,endolith/numpy,ahaldane/numpy,Eric89GXL/numpy,jakirkham/numpy,pbrod/numpy,Eric89GXL/numpy,jorisvandenbossche/numpy,WarrenWeckesser/numpy,MSeifert04/numpy,numpy/numpy,madphysicist/numpy,MSeifert04/numpy,shoyer/numpy,rgommers/numpy,pbrod/numpy,numpy/numpy,pbrod/numpy,anntzer/numpy,mhvk/numpy,WarrenWeckesser/numpy,MSeifert04/numpy,mhvk/numpy,ahaldane/numpy,jorisvandenbossche/numpy,madphysicist/numpy,mhvk/numpy,rgommers/numpy,grlee77/numpy,shoyer/numpy,endolith/numpy,simongibbons/numpy,madphysicist/numpy,WarrenWeckesser/numpy,mattip/numpy,pizzathief/numpy,grlee77/numpy,WarrenWeckesser/numpy,jakirkham/numpy,ahaldane/numpy,pbrod/numpy,shoyer/numpy,numpy/numpy,seberg/numpy,mhvk/numpy,mattip/numpy,jakirkham/numpy,charris/numpy,jorisvandenbossche/numpy,anntzer/numpy,pdebuyl/numpy,abalkin/numpy,grlee77/numpy,shoyer/numpy,pdebuyl/numpy,ahaldane/numpy,rgommers/numpy,pizzathief/numpy,gfyoung/numpy,simongibbons/numpy,pdebuyl/numpy,jorisvandenbossche/numpy,abalkin/numpy,pizzathief/numpy,grlee77/numpy,pizzathief/numpy,numpy/numpy,gfyoung/numpy,pdebuyl/numpy,seberg/numpy,simongibbons/numpy,charris/numpy,rgommers/numpy,WarrenWeckesser/numpy,MSeifert04/numpy,charris/numpy,madphysicist/numpy,anntzer/numpy,simongibbons/numpy,Eric89GXL/numpy,seberg/numpy,jorisvandenbossche/numpy,simongibbons/numpy,endolith/numpy,ahaldane/numpy,jakirkham/numpy,anntzer/numpy,pizzathief/numpy,mattip/numpy