Fix README link.
Fix README link.

Also add shell syntax highlighting.
taniarv/spree_digital,AnnArborTees/spree_digital,spree-contrib/spree_digital,taniarv/spree_digital,davekiss/spree_digital,denkungsart/solidus_digital,denkungsart/solidus_digital,denkungsart/solidus_digital,AnnArborTees/spree_digital,spree-contrib/spree_digital,brioux/spree_digital,AnnArborTees/spree_digital,spree-contrib/spree_digital,davekiss/spree_digital,brioux/spree_digital,brioux/spree_digital,taniarv/spree_digital