README: add a permission justification section (#36)

* README: add a permission justification section

* Fix format (#37)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

---------

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Author: massongit

README.md

@@ -17,6 +17,28 @@ These are inspired by [gcp-console-colorize](https://github.com/yfuruyama/gcp-co
 - Chrome: <https://chromewebstore.google.com/detail/aws-management-console-co/ihllnndjleheembkonidbocncnnedhcf>
 - Firefox: <https://addons.mozilla.org/ja/firefox/addon/aws-console-colorize/>
 
+## Permission justification
+
+### `storage` justification
+
+Those extensions save the colors of the AWS pages per session ARN to storage.
+
+### `tabs` justification
+
+The popup for those extensions sends messages to the content script running on the active tab to:
+
+- To get the session ARN used by the AWS pages.
+- If you change the settings in the popup, the settings will be reflected in the AWS pages.
+
+### Host permission justification
+
+<!-- textlint-disable ja-technical-writing/sentence-length -->
+
+The content script for those extensions is intended to work with the AWS management console and session selection page.  
+Therefore, the `content_scripts.matches` field is set to run only in the AWS management console and sign-in pages including session selection page.
+
+<!-- textlint-enable ja-technical-writing/sentence-length -->
+
 ## Development
 
 ### Settings