Add intro to traits section in traits_spec doc.
Add intro to traits section in traits_spec doc.

git-svn-id: 24f545668198cdd163a527378499f2123e59bf9f@1249 ead46cd0-7350-4e37-8683-fc4c6f79bf00

carlohamalainen/nipype,wanderine/nipype,FredLoney/nipype,glatard/nipype,carlohamalainen/nipype,mick-d/nipype_source,gerddie/nipype,sgiavasis/nipype,rameshvs/nipype,wanderine/nipype,sgiavasis/nipype,wanderine/nipype,pearsonlab/nipype,JohnGriffiths/nipype,grlee77/nipype,blakedewey/nipype,FCP-INDI/nipype,rameshvs/nipype,dgellis90/nipype,FredLoney/nipype,dgellis90/nipype,fprados/nipype,dgellis90/nipype,fprados/nipype,sgiavasis/nipype,satra/NiPypeold,FredLoney/nipype,Leoniela/nipype,arokem/nipype,carolFrohlich/nipype,mick-d/nipype_source,arokem/nipype,dmordom/nipype,FCP-INDI/nipype,Leoniela/nipype,blakedewey/nipype,glatard/nipype,Leoniela/nipype,dgellis90/nipype,rameshvs/nipype,wanderine/nipype,arokem/nipype,christianbrodbeck/nipype,iglpdc/nipype,mick-d/nipype_source,mick-d/nipype,mick-d/nipype,iglpdc/nipype,carolFrohlich/nipype,gerddie/nipype,JohnGriffiths/nipype,FCP-INDI/nipype,carlohamalainen/nipype,carolFrohlich/nipype,JohnGriffiths/nipype,pearsonlab/nipype,pearsonlab/nipype,grlee77/nipype,satra/NiPypeold,FCP-INDI/nipype,pearsonlab/nipype,carolFrohlich/nipype,JohnGriffiths/nipype,grlee77/nipype,christianbrodbeck/nipype,blakedewey/nipype,arokem/nipype,iglpdc/nipype,mick-d/nipype,blakedewey/nipype,fprados/nipype,mick-d/nipype,glatard/nipype,dmordom/nipype,glatard/nipype,gerddie/nipype,sgiavasis/nipype,dmordom/nipype,grlee77/nipype,iglpdc/nipype,gerddie/nipype,rameshvs/nipype