Readme additions.
Update README.md
updated docs for badges, added docs for webhooks
more badges.md changes - added put and delete, fixed the image upload section.
updated issuer docs to include new url schema
updated programs to use new url schema
Update README.md
Merge pull request #69 from mozilla/update-docs

Update docs
Update README.md
Update webhooks.md

Adding info about 'review' hook.
Update webhooks.md
Merge pull request #67 from mozilla/readme-update

Readme additions.