Update interceptors.md
Added the mention of public requirement!
@@ -32,6 +32,8 @@ Creating your own interceptors is easy. Custom interceptor classes do not need t
* The method may have any of the parameters specified for the given [Pointcut](/apidocs/hapi-fhir-base/ca/uhn/fhir/interceptor/api/Pointcut.html).
+* The method must be public.
+
The following example shows a simple request counter interceptor.
```java
