url: add missing documentation for URL.parse()

PR-URL: nodejs#53733
Reviewed-By: Matthew Aitken <maitken033380023@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

doc/api/url.md

@@ -691,6 +691,23 @@ const isValid = URL.canParse('/foo', 'https://example.org/'); // true
 const isNotValid = URL.canParse('/foo'); // false
 ```
 
+#### `URL.parse(input[, base])`
+
+<!-- YAML
+added: v22.1.0
+-->
+
+* `input` {string} The absolute or relative input URL to parse. If `input`
+  is relative, then `base` is required. If `input` is absolute, the `base`
+  is ignored. If `input` is not a string, it is [converted to a string][] first.
+* `base` {string} The base URL to resolve against if the `input` is not
+  absolute. If `base` is not a string, it is [converted to a string][] first.
+* Returns: {URL|null}
+
+Parses a string as a URL. If `base` is provided, it will be used as the base
+URL for the purpose of resolving non-absolute `input` URLs. Returns `null`
+if `input` is not a valid.
+
 ### Class: `URLSearchParams`
 
 <!-- YAML