Fix document for migrate-locations command (#1017)

## Changes
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#100 
#1006 
#1009 

### Functionality 

- [ ] added relevant user documentation
- [ ] added new CLI command
- [ ] modified existing command: `databricks labs ucx ...`
- [ ] added a new workflow
- [ ] modified existing workflow: `...`
- [ ] added a new table
- [ ] modified existing table: `...`

### Tests
<!-- How is this tested? Please see the checklist below and also
describe any other relevant tests -->

- [ ] manually tested
- [ ] added unit tests
- [ ] added integration tests
- [ ] verified on staging environment (screenshot attached)

Author: qziyuan

README.md

@@ -40,6 +40,7 @@ See [contributing instructions](CONTRIBUTING.md) to help improve this project.
   * [`create-uber-principal` command](#create-uber-principal-command)
   * [`migrate-credentials` command](#migrate-credentials-command)
   * [`validate-external-locations` command](#validate-external-locations-command)
+  * [`migrate-locations` command](#migrate-locations-command)
   * [`create-table-mapping` command](#create-table-mapping-command)
   * [`skip` command](#skip-command)
   * [`revert-migrated-tables` command](#revert-migrated-tables-command)
@@ -489,9 +490,9 @@ This command validates and provides mapping to external tables to external locat
 databricks labs ucx migrate-locations 
 ```
 
-Once the [`assessment` workflow](#assessment-workflow) finished successfully, and [storage credentials](#migrate-credentials-command) are configured, 
+Once the [`assessment` workflow](#assessment-workflow) finished successfully, and [storage credentials](#migrate-credentials-command) are configured,
 run this command to have Unity Catalog external locations created. The candidate locations to be created are extracted from guess_external_locations
-task in the assessment job. You can run `validate_external_locations` command to check the candidate locations.
+task in the assessment job. You can run [validate_external_locations](#validate-external-locations-command) command to check the candidate locations.
 
 [[back to top](#databricks-labs-ucx)]
 

labs.yml

@@ -134,5 +134,5 @@ commands:
       - name: workspace_ids
         description: List of workspace IDs to create account groups from.
 
-  - name: migrate_locations
+  - name: migrate-locations
     description: Create UC external locations based on the output of guess_external_locations assessment task.