Adding some additional json notes

README.md

@@ -56,6 +56,20 @@ Uses [CleanURLs](https://en.wikipedia.org/wiki/Clean_URL)
 
 The pattern `err := json.NewEncoder(w).Encode(data)` looks elegant but creates issues when needing to coditionally set headers in response to an error. The performance difference between `json.Marshal` and `json.Encoder` are so small(tiny more mem and 1 extra alloc) that it's just cleaner to use `json.Marshal`.
 
+### How Go Marshals JSON
+
+When Go is encoding a particular type to JSON, it looks to see if the type has a MarshalJSON() method implemented on it. If it has, then Go will call this method to determine how to encode it.
+
+
+Here is the interface
+```
+type Marshaler interface {
+    MarshalJSON() ([]byte, error)
+}
+```
+
+If the type doesn’t have a MarshalJSON() method, then Go will fall back to trying to encode it to JSON based on its own internal set of rules.
+
 ### Enveloping Respsonses