Adds requirement for matching account groups to be created before assessment to the docs (#4017)

## Changes
Account groups need to exist before assessment so that the crawl_groups
in the assessment finds and matches them to populate the groups table.

### Linked issues
Resolves #3451 

### Functionality
- [x] added relevant user documentation

Author: pritishpai

docs/ucx/docs/reference/workflows/index.mdx

@@ -12,13 +12,21 @@ steps of the [migration process](/docs/process). You can view the status of depl
 The assessment workflow can be triggered using the Databricks UI or via the
 [`ensure-assessment-run` command](/docs/reference/commands#ensure-assessment-run).
 
+> Account groups matching workspace local groups in which UCX is installed need to exist before running assessment.
+
+The account groups can be created in one of three ways:
+1. Manually created using the "Account Console".
+2. Using SCIM or other service utilizing the Account API.
+3. Using the [`create-account-groups` command](/docs/reference/commands#create-account-groups) command.
+
 The assessment workflow retrieves - or *crawls* - details of [workspace assets](https://docs.databricks.com/en/workspace/workspace-assets.html)
 and [securable objects in the Hive metastore](https://docs.databricks.com/en/data-governance/table-acls/object-privileges.html#securable-objects-in-the-hive-metastore)
 relevant for upgrading to UC to assess the compatibility with UC. The `crawl_` tasks retrieve assess and objects. The
 `assess_` tasks assess the compatibility with UC. The output of each task is stored in the
 [inventory database](/docs/installation#installation-resources) so that it can be used for further analysis and decision-making through
 the [assessment report](/docs/reference/assessment).
 
+
 1. `crawl_tables`: This task retrieves table definitions from the Hive metastore and persists the definitions in
    the `tables` table. The definitions include information such as:
    - Database/schema name
@@ -106,7 +114,7 @@ to manage groups from a single place: your Databricks account. We expect UCX use
 centrally while most other Databricks resources that UCX touches are scoped to a single workspace.
 For extra confidence, run [`validate-groups-membership` command](/docs/reference/commands#validate-groups-membership) before running the
 group migration. If you do not have account groups matching groups in the workspace in which UCX is installed, you can
-run [`create-account-groups` command](/docs/reference/commands#create-account-groups) before running the group migration workflow.
+run [`create-account-groups` command](/docs/reference/commands#create-account-groups) before running the assessment and group migration workflow.
 
 The group migration workflow is designed to migrate workspace-local groups to account-level groups. It verifies if
 the necessary groups are available to the workspace with the correct permissions, and removes unnecessary groups and