Update based on review comments.

Provider interface must add hook mechanism.
Make wording clearer.
Ensure Provider is listed alongside other hook registrars.

Signed-off-by: Justin Abrahms <jabrahms@ebay.com>

specification.json

@@ -266,8 +266,8 @@
         {
             "id": "Requirement 2.10",
             "machine_id": "requirement_2_10",
-            "content": "The provider interface MAY define a `provider hook` mechanism which can be optionally implemented in order to add `hook` instances to the client.",
-            "RFC 2119 keyword": "MAY",
+            "content": "The provider interface MUST define a `provider hook` mechanism which can be optionally implemented in order to add `hook` instances to the client.",
+            "RFC 2119 keyword": "MUST",
             "children": []
         },
         {
@@ -443,7 +443,7 @@
         {
             "id": "Requirement 4.4.1",
             "machine_id": "requirement_4_4_1",
-            "content": "The API, Client and invocation MUST have a method for registering hooks which accepts `flag evaluation options`",
+            "content": "The API, Client, Provider, and invocation MUST have a method for registering hooks.",
             "RFC 2119 keyword": "MUST",
             "children": []
         },

specification/sections/02-providers.md

@@ -113,11 +113,11 @@ ResolutionDetails<MyStruct> resolveStructureValue(string flagKey, MyStruct defau
 
 #### Provider hooks
 
-Feature flag management systems often need to transform the context structures the user provides or generally address lifecycle concerns. A `provider hook` exposes a mechanism for providers to register [`Hooks`](./04-hooks.md) to tap into various stages of the flag evaluation lifecycle.
+A `provider hook` exposes a mechanism for `providers` to register [`hooks`](./04-hooks.md) to tap into various stages of the flag evaluation lifecycle. As one example, feature flag management systems often need to transform the context structures the user provides.
 
 ##### Requirement 2.10
 
-> The provider interface **MAY** define a `provider hook` mechanism which can be optionally implemented in order to add `hook` instances to the client.
+> The provider interface **MUST** define a `provider hook` mechanism which can be optionally implemented in order to add `hook` instances to the client.
 
 ```
 class MyProvider implements Provider {

specification/sections/04-hooks.md

@@ -113,7 +113,7 @@ EvaluationContext | void before(HookContext, HookHints);
 
 #### Requirement 4.4.1
 
-> The API, Client and invocation **MUST** have a method for registering hooks which accepts `flag evaluation options`
+> The API, Client, Provider, and invocation **MUST** have a method for registering hooks.
 
 ```js
 OpenFeature.addHooks(new Hook1());