update intro text at https://author-tools.ietf.org/idnits

[ghwood]

Description

The old text has a number of grammatical nits and old links. New proposed text to address these:

I-D Diff (iddiff)

This service inspects Internet-Draft (I-D) documents for conditions that should be adjusted to bring the document into line with policies from the IETF, the IETF Trust, and the RFC Editor. Issues are reported based on:

• I-D Content Guidelines
• Additional requirements captured from Area Directors (ADs) and authors over time.
• Requirements in the original description of I-D Nits

Code of Conduct

• I agree to follow the IETF's Code of Conduct