docs: updated documentation for additional_packaging (#1907)

**Issue number:** Issue
[#1871](#1871)

### PR Type

**What kind of change does this PR introduce?**
* [ ] Feature
* [ ] Bug Fix
* [ ] Refactoring (no functional or API changes)
* [x] Documentation Update
* [ ] Maintenance (dependency updates, CI, etc.)

## Summary

### Changes

Updated the doc for `additional_packaging` to clearly mention where
should a developer place their `additional_packaging.py` file in their
source code.

### User experience

Documentation would be updated.

## Checklist

If an item doesn't apply to your changes, leave it unchecked.

### Review

* [x] self-review - I have performed a self-review of this change
according to the [development
guidelines](https://splunk.github.io/addonfactory-ucc-generator/contributing/#development-guidelines)
* [x] Changes are documented. The documentation is understandable,
examples work [(more
info)](https://splunk.github.io/addonfactory-ucc-generator/contributing/#documentation-guidelines)
* [x] PR title and description follows the [contributing
principles](https://splunk.github.io/addonfactory-ucc-generator/contributing/#pull-requests)
* [ ] meeting - I have scheduled a meeting or recorded a demo to explain
these changes (if there is a video, put a link below and in the ticket)

### Tests

See [the testing
doc](https://splunk.github.io/addonfactory-ucc-generator/contributing/#build-and-test).

* [ ] Unit - tests have been added/modified to cover the changes
* [ ] Smoke - tests have been added/modified to cover the changes
* [ ] UI - tests have been added/modified to cover the changes
* [ ] coverage - I have checked the code coverage of my changes [(see
more)](https://splunk.github.io/addonfactory-ucc-generator/contributing/#checking-the-code-coverage)

**Demo/meeting:**

*Reviewers are encouraged to request meetings or demos if any part of
the change is unclear*

Author: hetangmodi-crest

docs/additional_packaging.md

@@ -1,6 +1,6 @@
 # `additional_packaging.py` file
 
-To extend the build process, you can create a `additional_packaging.py` file in the same file level where you have your globalConfig file.
+To extend the build process, create a `additional_packaging.py` file in the root directory of your source code — that is, the same level where your package directory is located.
 
 This file should have either of the below two functions: