[github actions] install calibre

Author: swaroopch

.github/workflows/main.yml

@@ -9,6 +9,9 @@ jobs:
 
     steps:
 
+    - name: Install Calibre
+      run: sudo apt install calibre  # for `ebook-convert` command
+
     # https://github.com/actions/setup-node
     - name: Install Node.js
       uses: actions/[email protected]