Add clasp and prettier badges

README.ja.md

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 # Group Merge: Gmail のための差し込みメール作成 ([English](https://github.com/ttsukagoshi/mail-merge-for-gmail) / 日本語)
 
-[![Google Workspaceマーケットプレイスでこのアドオンを入手する](https://img.shields.io/badge/Google%20Workspace%20Add--on-Available-green)](https://workspace.google.com/marketplace/app/group_merge_mail_merge_for_gmail/586770229603) [![GitHub Super-Linter](https://github.com/ttsukagoshi/mail-merge-for-gmail/workflows/Lint%20Code%20Base/badge.svg)](https://github.com/marketplace/actions/super-linter)  
+[![Google Workspaceマーケットプレイスでこのアドオンを入手する](https://img.shields.io/badge/Google%20Workspace%20Add--on-Available-green?style=flat-square)](https://workspace.google.com/marketplace/app/group_merge_mail_merge_for_gmail/586770229603) [![GitHub Super-Linter](https://github.com/ttsukagoshi/mail-merge-for-gmail/workflows/Lint%20Code%20Base/badge.svg?style=flat-square)](https://github.com/marketplace/actions/super-linter) [![clasp](https://img.shields.io/badge/built%20with-clasp-4285f4.svg?style=flat-square)](https://github.com/google/clasp) [![code style: prettier](https://img.shields.io/badge/code_style-prettier-ff69b4.svg?style=flat-square)](https://github.com/prettier/prettier)
+
 Gmail と Google スプレッドシートを使って、受信者一人ひとり向けに宛名などを差し込んで作成。宛先リストで、宛先（メールアドレス）に重複がある場合、内容を 1 通のメールにまとめて送信できる **「まとめ差し込み（Group Merge）」** 機能つき。
 
 > **レガシー（スプレッドシート）版**  

README.md

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 # Group Merge: Mail Merge for Gmail (English / [日本語](https://github.com/ttsukagoshi/mail-merge-for-gmail/blob/main/README.ja.md))
 
-[![Get this add-on from Google Workspace Marketplace](https://img.shields.io/badge/Google%20Workspace%20Add--on-Available-green)](https://workspace.google.com/marketplace/app/group_merge_mail_merge_for_gmail/586770229603) [![GitHub Super-Linter](https://github.com/ttsukagoshi/mail-merge-for-gmail/workflows/Lint%20Code%20Base/badge.svg)](https://github.com/marketplace/actions/super-linter)  
+[![Get this add-on from Google Workspace Marketplace](https://img.shields.io/badge/Google%20Workspace%20Add--on-Available-green?style=flat-square)](https://workspace.google.com/marketplace/app/group_merge_mail_merge_for_gmail/586770229603) [![GitHub Super-Linter](https://github.com/ttsukagoshi/mail-merge-for-gmail/workflows/Lint%20Code%20Base/badge.svg?style=flat-square)](https://github.com/marketplace/actions/super-linter) [![clasp](https://img.shields.io/badge/built%20with-clasp-4285f4.svg?style=flat-square)](https://github.com/google/clasp) [![code style: prettier](https://img.shields.io/badge/code_style-prettier-ff69b4.svg?style=flat-square)](https://github.com/prettier/prettier)
+
 An open-sourced Google Workspace Add-on to send personalized emails based on Gmail template to multiple recipients using Google Sheets. The **Group Merge** feature allows the sender to group the contents of two or more rows into one row for a single recipient.
 
 > **Legacy Spreadsheet Version**