Added deprecation guide about Ember.computed.any

[phkavitha]

My first commit towards fixing #2256.

[wycats]

@phkavitha Thanks for submitting this. I look forward to merging it.

A couple of things:

1. We use American spelling for favor (o rather than ou).
2. We generally add a colon to a sentence that is immediately followed by an example (For example: rather than For example,).
3. The reason we changed from any to or is to reflect the fact that the computed value is the first successful value (like ||) rather than a boolean (like Array.prototype.any). It might be useful to include that information.

Thanks so much again for the contribution!

[wycats]

Also, can you rebase?

[phkavitha]

@wycats , I have made the necessary changes. Let me know if any changes are required. Thanks for your help.

[rwjblue]

Thank you!