DOC: warning section on memory overflow when joining/merging dataframes on index with duplicate keys (#14788)
DOC: warning section on memory overflow when joining/merging dataframes on index with duplicate keys (#14788)

closes #14736
jreback/pandas,cython-testbed/pandas,harisbal/pandas,cbertinato/pandas,dsm054/pandas,jmmease/pandas,harisbal/pandas,cython-testbed/pandas,cbertinato/pandas,louispotok/pandas,linebp/pandas,TomAugspurger/pandas,TomAugspurger/pandas,datapythonista/pandas,zfrenchee/pandas,nmartensen/pandas,pratapvardhan/pandas,datapythonista/pandas,cython-testbed/pandas,winklerand/pandas,pratapvardhan/pandas,DGrady/pandas,Winand/pandas,jreback/pandas,dsm054/pandas,louispotok/pandas,amolkahat/pandas,kdebrab/pandas,GuessWhoSamFoo/pandas,pandas-dev/pandas,MJuddBooth/pandas,gfyoung/pandas,Winand/pandas,nmartensen/pandas,dsm054/pandas,jorisvandenbossche/pandas,amolkahat/pandas,cbertinato/pandas,datapythonista/pandas,GuessWhoSamFoo/pandas,harisbal/pandas,jmmease/pandas,jorisvandenbossche/pandas,linebp/pandas,dsm054/pandas,pratapvardhan/pandas,DGrady/pandas,zfrenchee/pandas,harisbal/pandas,toobaz/pandas,TomAugspurger/pandas,jmmease/pandas,Winand/pandas,toobaz/pandas,jmmease/pandas,jorisvandenbossche/pandas,pratapvardhan/pandas,amolkahat/pandas,gfyoung/pandas,linebp/pandas,rs2/pandas,winklerand/pandas,kdebrab/pandas,rs2/pandas,jreback/pandas,rs2/pandas,gfyoung/pandas,jorisvandenbossche/pandas,GuessWhoSamFoo/pandas,rs2/pandas,linebp/pandas,MJuddBooth/pandas,TomAugspurger/pandas,jreback/pandas,winklerand/pandas,zfrenchee/pandas,GuessWhoSamFoo/pandas,nmartensen/pandas,nmartensen/pandas,MJuddBooth/pandas,winklerand/pandas,pandas-dev/pandas,cbertinato/pandas,zfrenchee/pandas,dsm054/pandas,cython-testbed/pandas,MJuddBooth/pandas,louispotok/pandas,amolkahat/pandas,kdebrab/pandas,jmmease/pandas,pandas-dev/pandas,toobaz/pandas,cython-testbed/pandas,winklerand/pandas,toobaz/pandas,GuessWhoSamFoo/pandas,DGrady/pandas,zfrenchee/pandas,DGrady/pandas,nmartensen/pandas,toobaz/pandas,gfyoung/pandas,pandas-dev/pandas,louispotok/pandas,louispotok/pandas,Winand/pandas,linebp/pandas,harisbal/pandas,winklerand/pandas,kdebrab/pandas,datapythonista/pandas,kdebrab/pandas,Winand/pandas,pratapvardhan/pandas,amolkahat/pandas,DGrady/pandas,cbertinato/pandas,nmartensen/pandas,gfyoung/pandas,jreback/pandas,jmmease/pandas,DGrady/pandas,linebp/pandas,MJuddBooth/pandas,Winand/pandas