Tweak some wording

update graphql docs

changelogs/unreleased/262857-creation-rotation-graphql.yml

 ---
-title: Add create On-call rotations GraphQL mutation
+title: Add GraphQL mutation to create on-call rotations
 merge_request: 49206
 author:
 type: added

doc/api/graphql/reference/gitlab_schema.graphql

@@ -15710,7 +15710,7 @@ input OncallRotationCreateInput {
   rotationLength: OncallRotationLengthInputType!
 
   """
-  The iid of the on-call schedule to create the on-call rotation in.
+  The IID of the on-call schedule to create the on-call rotation in.
   """
   scheduleIid: String!
 
@@ -15950,7 +15950,7 @@ input OncallUserInputType {
   colorWeight: DataVisualizationWeightEnum
 
   """
-  The username of the user to participate in the on-call rotation. i.e user_one.
+  The username of the user to participate in the on-call rotation, such as `user_one`.
   """
   username: String!
 }

doc/api/graphql/reference/gitlab_schema.json

@@ -46622,7 +46622,7 @@
             },
             {
               "name": "scheduleIid",
-              "description": "The iid of the on-call schedule to create the on-call rotation in.",
+              "description": "The IID of the on-call schedule to create the on-call rotation in.",
               "type": {
                 "kind": "NON_NULL",
                 "name": null,
@@ -47297,7 +47297,7 @@
           "inputFields": [
             {
               "name": "username",
-              "description": "The username of the user to participate in the on-call rotation. i.e user_one.",
+              "description": "The username of the user to participate in the on-call rotation, such as `user_one`.",
               "type": {
                 "kind": "NON_NULL",
                 "name": null,

ee/app/graphql/mutations/incident_management/oncall_rotation/create.rb

@@ -14,7 +14,7 @@ module Mutations
 
         argument :schedule_iid, GraphQL::STRING_TYPE,
                  required: true,
-                 description: 'The iid of the on-call schedule to create the on-call rotation in.',
+                 description: 'The IID of the on-call schedule to create the on-call rotation in.',
                  as: :iid
 
         argument :name, GraphQL::STRING_TYPE,
@@ -104,7 +104,7 @@ module Mutations
         end
 
         def raise_user_not_found
-          raise Gitlab::Graphql::Errors::ArgumentError, 'A username that was provided could not be matched to a user'
+          raise Gitlab::Graphql::Errors::ArgumentError, "A provided username couldn't be matched to a user"
         end
       end
     end

ee/app/graphql/types/incident_management/oncall_user_input_type.rb

@@ -9,7 +9,7 @@ module Types
 
       argument :username, GraphQL::STRING_TYPE,
                 required: true,
-                description: 'The username of the user to participate in the on-call rotation. i.e user_one.'
+                description: 'The username of the user to participate in the on-call rotation, such as `user_one`.'
 
       argument :color_palette, ::Types::DataVisualizationPalette::ColorEnum,
                 required: false,

ee/spec/graphql/mutations/incident_management/oncall_rotation/create_spec.rb

@@ -66,7 +66,7 @@ RSpec.describe Mutations::IncidentManagement::OncallRotation::Create do
           end
 
           it 'raises an error' do
-            expect { resolve }.to raise_error(Gitlab::Graphql::Errors::ArgumentError, 'A username that was provided could not be matched to a user')
+            expect { resolve }.to raise_error(Gitlab::Graphql::Errors::ArgumentError, "A provided username couldn't be matched to a user")
           end
         end