Fix typos in doc files
Fix typos in doc files

Summary:
I was reading through the doc files and found some typos. Thought of sending out
the fix for them instead of letting them stay there :)

Reviewed By: aeckert

Differential Revision: D3159824

fb-gh-sync-id: 327b1685b5d067b572713e9aa02c771fba400fd7
fbshipit-source-id: 327b1685b5d067b572713e9aa02c771fba400fd7

neuhausler/fboss,peterlei/fboss,neuhausler/fboss,neuhausler/fboss,peterlei/fboss,peterlei/fboss,neuhausler/fboss,peterlei/fboss