Create send-as-email under "share" in the docs

- Explains how to use "send as email
- Explains how to attach linked files to your email message

en/collaborative-work/send-as-email

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+# Send as Email
+
+JabRef allows you to send entries to third parties via email.
+
+### How to send as e-mail:
+
+1. Select one or multiple entries
+2. Choose **Tools → Send as email** in the menu
+
+This will open your default email application and automatically paste the entries in their raw BibTeX format.
+Once your correspondents have received the email, they will be able to directly copy and paste the entries into JabRef (or use them in other ways).
+
+## How to attach linked files of entries to your email
+
+Once `Send as email` is pressed, JabRef will also automatically open the folder of attached files, as long as the option `automatically open folders of attached files` is enabled at **File → Preferences → External programs → Sending of emails**.
+Attaching these files to your email is possible by dragging and dropping the pdf files into your favourite email application.