[docs] update TravisCI badge and intro
[docs] update TravisCI badge and intro

tj93/pymtl,cornell-brg/pymtl,jck/pymtl,jck/pymtl,cornell-brg/pymtl,tj93/pymtl,12yujim/pymtl,cfelton/pymtl,Glyfina-Fernando/pymtl,jck/pymtl,12yujim/pymtl,cfelton/pymtl,Glyfina-Fernando/pymtl,tj93/pymtl,cfelton/pymtl,jjffryan/pymtl,12yujim/pymtl,jjffryan/pymtl,jjffryan/pymtl,Glyfina-Fernando/pymtl,cornell-brg/pymtl