Add imap-send to the list of email helpers

git imap-send is a git command that enables a person to send an email in mbox format generated by git format-patch to a folder using IMAP.

Its link was missing from https://git-scm.com/docs

Author: AdityaGarg8

data/doc_categories/email.yml

@@ -4,6 +4,7 @@ name: "Email"
 commands:
   - doc: "git-am"
   - doc: "git-apply"
+  - doc: "git-imap-send"
   - doc: "git-format-patch"
   - doc: "git-send-email"
   - doc: "git-request-pull"