DOCS: add dhcid RR docs (#2715)

documentation/functions/domain/DHCID.md

@@ -0,0 +1,23 @@
+---
+name: DHCID
+parameters:
+  - name
+  - digest
+  - modifiers...
+parameter_types:
+  name: string
+  digest: string
+  "modifiers...": RecordModifier[]
+---
+
+DHCID adds a DHCID record to the domain.
+
+Digest should be a string.
+
+{% code title="dnsconfig.js" %}
+```javascript
+D("example.com", REG_MY_PROVIDER, DnsProvider(DSP_MY_PROVIDER),
+  DHCID("example.com", "ABCDEFG")
+);
+```
+{% endcode %}