Reformat contributing guidelines to make them less nested
Reformat contributing guidelines to make them less nested

xref GH9754, GH9796

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