DOC: Improve documentation of common_type (#9344)
DOC: Improve documentation of common_type (#9344)

Fixes gh-9326
gfyoung/numpy,tynn/numpy,mhvk/numpy,jorisvandenbossche/numpy,tynn/numpy,grlee77/numpy,endolith/numpy,abalkin/numpy,bringingheavendown/numpy,jorisvandenbossche/numpy,Eric89GXL/numpy,b-carter/numpy,anntzer/numpy,anntzer/numpy,jakirkham/numpy,shoyer/numpy,tynn/numpy,numpy/numpy,solarjoe/numpy,solarjoe/numpy,MSeifert04/numpy,jakirkham/numpy,numpy/numpy,seberg/numpy,pdebuyl/numpy,shoyer/numpy,pizzathief/numpy,grlee77/numpy,simongibbons/numpy,ahaldane/numpy,gfyoung/numpy,pbrod/numpy,pdebuyl/numpy,MSeifert04/numpy,endolith/numpy,madphysicist/numpy,bringingheavendown/numpy,pdebuyl/numpy,mattip/numpy,charris/numpy,endolith/numpy,charris/numpy,MSeifert04/numpy,b-carter/numpy,bringingheavendown/numpy,mhvk/numpy,pdebuyl/numpy,Eric89GXL/numpy,madphysicist/numpy,seberg/numpy,rgommers/numpy,ahaldane/numpy,simongibbons/numpy,simongibbons/numpy,solarjoe/numpy,mattip/numpy,gfyoung/numpy,pizzathief/numpy,WarrenWeckesser/numpy,pbrod/numpy,MSeifert04/numpy,numpy/numpy,ahaldane/numpy,WarrenWeckesser/numpy,anntzer/numpy,WarrenWeckesser/numpy,rgommers/numpy,anntzer/numpy,madphysicist/numpy,MSeifert04/numpy,shoyer/numpy,pizzathief/numpy,madphysicist/numpy,jorisvandenbossche/numpy,simongibbons/numpy,pbrod/numpy,charris/numpy,grlee77/numpy,jorisvandenbossche/numpy,seberg/numpy,jorisvandenbossche/numpy,madphysicist/numpy,jakirkham/numpy,grlee77/numpy,WarrenWeckesser/numpy,ahaldane/numpy,b-carter/numpy,simongibbons/numpy,endolith/numpy,abalkin/numpy,pbrod/numpy,jakirkham/numpy,mhvk/numpy,mattip/numpy,abalkin/numpy,Eric89GXL/numpy,pizzathief/numpy,numpy/numpy,charris/numpy,grlee77/numpy,shoyer/numpy,jakirkham/numpy,Eric89GXL/numpy,rgommers/numpy,rgommers/numpy,mhvk/numpy,seberg/numpy,pizzathief/numpy,mhvk/numpy,shoyer/numpy,pbrod/numpy,WarrenWeckesser/numpy,mattip/numpy,ahaldane/numpy