Add instructions in README

Author: talee

README.md

@@ -1,2 +1,77 @@
 # validate-http-headers
-Utility to validate HTTP headers of multiple URL based on a JSON spec
+Utility to validate HTTP headers of multiple URLs based on a JSON spec. Useful
+to quickly set default request headers and automate network deployment testing.
+
+Write a JSON spec file for the validator to use: e.g. urls.json
+
+Pass it to the validator
+
+	$ ./validate-http-headers urls.json
+
+    ------------------------------------------------------------------------
+    FILE: urls.json
+    
+    URL: https://www.google.com/
+    SUCCESS: Expected 'X-Frame-Options' to have 'SAMEORIGIN' match 'SAMEORIGIN'
+    SUCCESS: Expected 'Expires' to have '-1' match '-1'
+    
+    URL: https://drive.google.com/
+    SUCCESS: Response header 'X-Frame-Options' should not exist
+
+Multiple JSON specs can be passed
+
+	$ ./validate-http-headers internal.json external.json mtv.json
+
+Simple spec:
+
+    {
+      "default": {
+        "requestHeaders": {
+          "Referer": ["https://bad-website.com"]
+        },
+        "responseHeaders": {
+          "X-Frame-Options": ["SAMEORIGIN"]
+        }
+      },
+    
+      "specs": [
+        {
+          "url": "https://www.google.com/"
+        },
+        {
+          "url": "https://drive.google.com/"
+        }
+      ]
+    }
+
+Complex spec with overrides:
+
+    {
+      "default": {
+        "requestHeaders": {
+          "Referer": ["https://golang.org"]
+        },
+        "responseHeaders": {
+          "X-Frame-Options": ["SAMEORIGIN"]
+        }
+      },
+    
+      "specs": [
+        {
+          "url": "https://www.google.com/",
+          "requestHeaders": {
+            "Referer": ["https://drive.google.com"]
+          },
+          "responseHeaders": {
+            "Expires": ["-1"]
+          }
+        },
+        {
+          "url": "https://drive.google.com/",
+          "responseHeaders": {
+            "X-Frame-Options": [""]
+          }
+        }
+      ]
+    }
+