Incorrect namespace URI in example

[gbicann]

The example XML instance in the dkhm:delDate section of README.md has an error:

<extension>
    <dkhm:delDate xmlns:dkhm="urn:dkhm:xml:ns:dkhm-4.4">2021-01-31T00:00:00.0Z</dkhm:delDate>
</extension>

should be

<extension>
    <dkhm:delDate xmlns:dkhm="urn:dkhm:params:xml:ns:dkhm-4.4">2021-01-31T00:00:00.0Z</dkhm:delDate>
</extension>

Also, please note that URN namespace prefixes (such as urn:dkhm:) should be registered with IANA, as per Section 6 of RFC 8141.