[CAIP-10] Editorial: minor wordsmithing in ## Canonicalization section

[bumblefudge]

Minor and non-normative.

This is just to draw more attention to the changes being made in namespaces#122, following implementer feedback that the checksum-case/lowercase difference wasn't explicit enough.

If this feels like too much to change on a "Final"-status CAIP, even though it's non-normative and purely editorial, we could go the #288 route and just publish an informational CAIP as a "BCP"-style update. Feels a little overkill to do that just to make the wording clearer, though.

[obstropolos]

Approved, but I want @pedrouid to give this a quick glance as well.

[bumblefudge]

@pedrouid 👋

[bumblefudge]

@pedrouid quick review?