Add Curling For Headers as a unix til

unix/curling-for-headers.md

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+# Curling For Headers
+
+If you want to inspect the headers of a response from some endpoint, look no
+further than a quick `curl` command. By including the `-I` flag, `curl` will
+return just the headers.
+
+For example, if you are developing a web app that is being locally served at
+`localhost:3000` and you'd like to see what the headers look like for a
+particular URL, you might try something like the following command:
+
+```bash
+$ curl -I localhost:3000/posts
+```
+
+h/t Dillon Hafer