GraphQL: Order mutation docs into sections

doc/development/api_graphql_styleguide.md

@@ -708,19 +708,6 @@ To find objects for a mutation, arguments need to be specified. As with
 [resolvers](#resolvers), prefer using internal ID or, if needed, a
 global ID rather than the database ID.
 
-### Fields
-
-In the most common situations, a mutation would return 2 fields:
-
-- The resource being modified
-- A list of errors explaining why the action could not be
-  performed. If the mutation succeeded, this list would be empty.
-
-By inheriting any new mutations from `Mutations::BaseMutation` the
-`errors` field is automatically added. A `clientMutationId` field is
-also added, this can be used by the client to identify the result of a
-single mutation when multiple are performed within a single request.
-
 ### Building Mutations
 
 Mutations live in `app/graphql/mutations` ideally grouped per
@@ -728,12 +715,16 @@ resources they are mutating, similar to our services. They should
 inherit `Mutations::BaseMutation`. The fields defined on the mutation
 will be returned as the result of the mutation.
 
+### Naming conventions
+
 Always provide a consistent GraphQL-name to the mutation, this name is
 used to generate the input types and the field the mutation is mounted
 on. The name should look like `<Resource being modified><Mutation
 class name>`, for example the `Mutations::MergeRequests::SetWip`
 mutation has GraphQL name `MergeRequestSetWip`.
 
+### Arguments
+
 Arguments required by the mutation can be defined as arguments
 required for a field. These will be wrapped up in an input type for
 the mutation. For example, the `Mutations::MergeRequests::SetWip`
@@ -762,11 +753,28 @@ This would automatically generate an input type called
 `clientMutationId`.
 
 These arguments are then passed to the `resolve` method of a mutation
-as keyword arguments. From here, we can call the service that will
-modify the resource.
+as keyword arguments.
+
+### Fields
+
+In the most common situations, a mutation would return 2 fields:
+
+- The resource being modified
+- A list of errors explaining why the action could not be
+  performed. If the mutation succeeded, this list would be empty.
+
+By inheriting any new mutations from `Mutations::BaseMutation` the
+`errors` field is automatically added. A `clientMutationId` field is
+also added, this can be used by the client to identify the result of a
+single mutation when multiple are performed within a single request.
+
+### The `resolve` method
+
+The `resolve` method receives the mutation's arguments as keyword arguments.
+From here, we can call the service that will modify the resource.
 
 The `resolve` method should then return a hash with the same field
-names as defined on the mutation and an `errors` array. For example,
+names as defined on the mutation including an `errors` array. For example,
 the `Mutations::MergeRequests::SetWip` defines a `merge_request`
 field:
 
@@ -791,7 +799,9 @@ should look like this:
 }
 ```
 
-To make the mutation available it should be defined on the mutation
+### Mounting the mutation
+
+To make the mutation available it must be defined on the mutation
 type that lives in `graphql/types/mutation_types`. The
 `mount_mutation` helper method will define a field based on the
 GraphQL-name of the mutation: