DOCS: add docs for NS1_URLFWD (#3075)

Co-authored-by: Tom Limoncelli <tlimoncelli@stackoverflow.com>

documentation/language-reference/domain-modifiers/NS1_URLFWD.md

@@ -11,6 +11,28 @@ parameter_types:
   "modifiers...": RecordModifier[]
 ---
 
-{% hint style="info" %}
+`NS1_URLFWD` is an NS1-specific feature that maps to NS1's URLFWD record, which creates HTTP 301 (permanent) or 302 (temporary) redirects.
-Documentation needed.
+
+
+{% code title="dnsconfig.js" %}
+```javascript
+D("example.com", REG_MY_PROVIDER, DnsProvider(DSP_MY_PROVIDER),
+  NS1_URLFWD("urlfwd", "/ http://example.com 302 2 0")
+);
+```
+{% endcode %}
+
+The fields are:
+* name: the record name
+* target: a complex field containing the following, space separated:
+    * from - the path to match
+    * to - the url to redirect to
+    * redirectType - (0 - masking, 301, 302)
+    * pathForwardingMode - (0 - All, 1 - Capture, 2 - None)
+    * queryForwardingMode - (0 - disabled, 1 - enabled)
+
+{% hint style="warning" %}
+**WARNING**: According to NS1, this type of record is deprecated and in the process
+of being replaced by the premium-only `REDIRECT` record type. While still able to be
+configured through the API, as suggested by NS1, please try not to use it, going forward.
 {% endhint %}