[Openid-specs-fapi] Issue #561: Intro need to be fixed (openid/fapi)

[Nat]

New issue 561: Intro need to be fixed
https://bitbucket.org/openid/fapi/issues/561/intro-need-to-be-fixed

Nat Sakimura:

The introduction just gives legal statements and is not helpful for readers to understand what this document is. 

Aligning with the structure of [https://openid.bitbucket.io/fapi/fapi-2\_0-security-profile.html](https://openid.bitbucket.io/fapi/fapi-2_0-security-profile.html) would be advisable.