In the introduction add a couple of paragraphs explaining the various sections.
Richard Ishida suggested that.
Should maybe also explain the history a little bit with (non-normative, doh) pointers to IANA charset, old RFCs, old unicode.org stuff.
Here is a sketch for what this could be. I don't really like it.
The section "Encodings" defines the general structure of an encoding, including its decoder and encoder functionality. As well as defining the full list of labels, the encodings they map to, and an algorithm for obtaining an encoding from a presumed label.
The section "Indexes" defines the general structure of an index, used by an encoding's decoder and encoder, and lists the indexes used by encodings that use more than one byte to encode certain code points.
The section "Decode and encode" defines entry points for use by other standards.
The remaining sections define the decoder and encoder algorithms of the encodings.