docs(readme): update migration guide

Author: apaparazzi0329

MIGRATION-V7.md

@@ -20,27 +20,28 @@
 - QueryAggregation classes restructured
 
 #### Natural Language Understanding
-- All `sentimentModel` functions removed
+- All `sentiment_model` functions removed
+- `create_classifications_model`, `update_classifications_model`, `create_categories_model`, and `update_categories_model` now require `training_data_content_type`
 
 #### Speech to Text
 - `AR_AR_BROADBANDMODEL` model removed in favor of `AR_MS_BROADBANDMODEL` model
 
 ### New Features by Service
 
 #### Assistant v2
-- `createAssistant` function
-- `listAssistants` function
-- `deleteAssistant` function
-- `updateEnvironment` function
-- `createRelease` function
-- `deleteRelease` function
-- `getSkill` function
-- `updateSkill` function
-- `exportSkills` function
-- `importSkills` function
-- `importSkillsStatus` function
+- `create_assistant` function
+- `list_assistants` function
+- `delete_assistant` function
+- `update_environment` function
+- `create_release` function
+- `delete_release` function
+- `get_skill` function
+- `update_skill` function
+- `export_skills` function
+- `import_skills` function
+- `import_skills_status` function
 - Improved typing for `message` function call
-See details of these functions on IBM's documentation site [here](https://cloud.ibm.com/apidocs/assistant-v2?code=node)
+See details of these functions on IBM's documentation site [here](https://cloud.ibm.com/apidocs/assistant-v2?code=python)
 
 #### Discovery v2
 - Aggregation types `QueryTopicAggregation` and `QueryTrendAggregation` added
@@ -50,5 +51,5 @@ See details of these functions on IBM's documentation site [here](https://cloud.
 
 #### Text to Speech
 - added `EN_AU_HEIDIEXPRESSIVE`, `EN_AU_JACKEXPRESSIVE`, `EN_US_ALLISONEXPRESSIVE`, `EN_US_EMMAEXPRESSIVE`, `EN_US_LISAEXPRESSIVE`, `EN_US_MICHAELEXPRESSIVE`, `KO_KR_JINV3VOICE`
-- Parameters `ratePercentage` and `pitchPercentage` added to `synthesize` function
-See details of these new parameters on IBM's documentation site [here](https://cloud.ibm.com/apidocs/text-to-speech?code=node#synthesize)
+- Parameters `rate_percentage` and `pitch_percentage` added to `synthesize` function
+See details of these new parameters on IBM's documentation site [here](https://cloud.ibm.com/apidocs/text-to-speech?code=python#synthesize)