DOC: Spell out note for `hstack`
DOC: Spell out note for `hstack`

This adds to the documentation on `hstack` the note from `vstack` about the dimensionality requirement.
jorisvandenbossche/numpy,ahaldane/numpy,bringingheavendown/numpy,ahaldane/numpy,abalkin/numpy,solarjoe/numpy,simongibbons/numpy,abalkin/numpy,madphysicist/numpy,shoyer/numpy,numpy/numpy,pdebuyl/numpy,solarjoe/numpy,behzadnouri/numpy,seberg/numpy,endolith/numpy,mhvk/numpy,numpy/numpy,pizzathief/numpy,tynn/numpy,mhvk/numpy,shoyer/numpy,charris/numpy,mattip/numpy,anntzer/numpy,MSeifert04/numpy,charris/numpy,jakirkham/numpy,shoyer/numpy,abalkin/numpy,jorisvandenbossche/numpy,shoyer/numpy,mattip/numpy,behzadnouri/numpy,mhvk/numpy,pizzathief/numpy,simongibbons/numpy,grlee77/numpy,WarrenWeckesser/numpy,MSeifert04/numpy,pbrod/numpy,pizzathief/numpy,anntzer/numpy,grlee77/numpy,MSeifert04/numpy,Eric89GXL/numpy,Eric89GXL/numpy,grlee77/numpy,pbrod/numpy,b-carter/numpy,bringingheavendown/numpy,WarrenWeckesser/numpy,madphysicist/numpy,numpy/numpy,charris/numpy,mattip/numpy,endolith/numpy,pizzathief/numpy,pbrod/numpy,WarrenWeckesser/numpy,chatcannon/numpy,WarrenWeckesser/numpy,behzadnouri/numpy,solarjoe/numpy,jakirkham/numpy,madphysicist/numpy,jakirkham/numpy,gfyoung/numpy,grlee77/numpy,pbrod/numpy,b-carter/numpy,chatcannon/numpy,endolith/numpy,mattip/numpy,b-carter/numpy,Eric89GXL/numpy,bringingheavendown/numpy,charris/numpy,ahaldane/numpy,pdebuyl/numpy,rgommers/numpy,rgommers/numpy,pdebuyl/numpy,jorisvandenbossche/numpy,MSeifert04/numpy,anntzer/numpy,seberg/numpy,endolith/numpy,jorisvandenbossche/numpy,mhvk/numpy,pizzathief/numpy,tynn/numpy,rgommers/numpy,seberg/numpy,gfyoung/numpy,madphysicist/numpy,pdebuyl/numpy,Eric89GXL/numpy,simongibbons/numpy,chatcannon/numpy,grlee77/numpy,jakirkham/numpy,madphysicist/numpy,ahaldane/numpy,gfyoung/numpy,anntzer/numpy,ahaldane/numpy,jakirkham/numpy,seberg/numpy,jorisvandenbossche/numpy,numpy/numpy,mhvk/numpy,tynn/numpy,simongibbons/numpy,rgommers/numpy,WarrenWeckesser/numpy,pbrod/numpy,MSeifert04/numpy,simongibbons/numpy,shoyer/numpy