doc: updated wildcard debuglog example on util

Author: TylerYang

doc/api/util.md

@@ -104,6 +104,19 @@ FOO 3245: hello from foo [123]
 where `3245` is the process id.  If it is not run with that
 environment variable set, then it will not print anything.
 
+The `section` supports wildcard also, for example:
+```js
+const util = require('util');
+const debuglog = util.debuglog('foo-bar');
+
+debuglog('hi there, it\'s foo-bar [%d]', 2333);
+```
+
+if it is run with `NODE_DEBUG=foo*` in the environment, then it will output something like:
+```txt
+FOO-BAR 3257: hi there, it's foo-bar [2333]
+```
+
 Multiple comma-separated `section` names may be specified in the `NODE_DEBUG`
 environment variable. For example: `NODE_DEBUG=fs,net,tls`.