Guides: Missing erb tags for stylesheet_pack_tag [ci skip]
Guides: Missing erb tags for stylesheet_pack_tag [ci skip]

The section on needing to use `stylesheet_pack_tag` was lacking the erb
%'s.

I updated the markdown to actually show the helper being used with erb
as well as improve the wording of the sentence.

BlakeWilliams/rails,georgeclaghorn/rails,georgeclaghorn/rails,joonyou/rails,esparta/rails,Edouard-chin/rails,rails/rails,rails/rails,yawboakye/rails,Stellenticket/rails,kmcphillips/rails,Edouard-chin/rails,Stellenticket/rails,Vasfed/rails,Stellenticket/rails,Stellenticket/rails,bogdanvlviv/rails,EmmaB/rails-1,Envek/rails,georgeclaghorn/rails,MSP-Greg/rails,georgeclaghorn/rails,kddeisz/rails,EmmaB/rails-1,MSP-Greg/rails,bogdanvlviv/rails,Edouard-chin/rails,yawboakye/rails,esparta/rails,Edouard-chin/rails,MSP-Greg/rails,yahonda/rails,BlakeWilliams/rails,joonyou/rails,bogdanvlviv/rails,Envek/rails,Erol/rails,yahonda/rails,Envek/rails,lcreid/rails,Erol/rails,MSP-Greg/rails,betesh/rails,rails/rails,joonyou/rails,kddeisz/rails,betesh/rails,Erol/rails,betesh/rails,yawboakye/rails,lcreid/rails,Vasfed/rails,Vasfed/rails,yawboakye/rails,esparta/rails,lcreid/rails,bogdanvlviv/rails,kddeisz/rails,BlakeWilliams/rails,esparta/rails,betesh/rails,Envek/rails,yahonda/rails,kmcphillips/rails,Vasfed/rails,joonyou/rails,BlakeWilliams/rails,Erol/rails,yahonda/rails,kmcphillips/rails,kddeisz/rails,rails/rails,kmcphillips/rails,lcreid/rails,EmmaB/rails-1