Fixing broken link
Mention that Ember prototype extensions are optional early.
Merge pull request #841 from pwnall/prototype-panic

Mention that Ember prototype extensions are optional early.
Grammar nits.
Merge pull request #842 from pwnall/grammar

Grammar nits.
fixes wrong url, "Tag: V1.0.0", left navigation bar
Merge pull request #843 from twokul/master

fixes wrong url, "Tag: V1.0.0", left navigation bar
Updated the contributing section of the cookbook.
Merge pull request #840 from vineet-sinha/patch-1

Fixing broken link
Revert "Mention that Ember prototype extensions are optional early."

This reverts commit b907a351e809c981de7e354002ebae0491c1e8c5.

As mentioned in
https://github.com/emberjs/website/pull/841#issuecomment-24073977 these
guides are meant for information that nearly all consumers of the
framework will need. We likely need to add a 'further reading' section
or something.