Add shell to preformatted blocks in readme.
Add shell to preformatted blocks in readme.

Reviewed at https://reviews.apache.org/r/31864/

medallia/aurora,rdelval/aurora,rosmo/aurora,protochron/aurora,medallia/aurora,rosmo/aurora,medallia/aurora,wfarner/aurora,kidaa/aurora,crashlytics/aurora,rdelval/aurora,thinker0/aurora,shahankhatch/aurora,protochron/aurora,thinker0/aurora,mschenck/aurora,protochron/aurora,crashlytics/aurora,medallia/aurora,kidaa/aurora,rdelval/aurora,shahankhatch/aurora,wfarner/aurora,crashlytics/aurora,rosmo/aurora,rdelval/aurora,mschenck/aurora,apache/aurora,shahankhatch/aurora,crashlytics/aurora,rosmo/aurora,thinker0/aurora,apache/aurora,mschenck/aurora,wfarner/aurora,wfarner/aurora,wfarner/aurora,kidaa/aurora,rdelval/aurora,rosmo/aurora,apache/aurora,apache/aurora,thinker0/aurora,medallia/aurora,protochron/aurora,thinker0/aurora,mschenck/aurora,crashlytics/aurora,kidaa/aurora,mschenck/aurora,shahankhatch/aurora,shahankhatch/aurora,apache/aurora,medallia/aurora,rosmo/aurora,mschenck/aurora,protochron/aurora,rdelval/aurora,kidaa/aurora,shahankhatch/aurora,thinker0/aurora,crashlytics/aurora,wfarner/aurora,kidaa/aurora,apache/aurora,protochron/aurora