docs: Add macro for import docs "logging in" section.

Fixes #9550.

templates/zerver/help/import-data-from-slack.md

@@ -60,28 +60,7 @@ cd /home/zulip/deployments/current
 ./manage.py import --import-into-nonempty <subdomain> converted_slack_data
 ```
 
-## Logging in
-
-Once the import completes, all your users will have accounts in your
-new Zulip organization, but those accounts won't have passwords yet
-(since for very good security reasons, passwords are not exported).
-Your users will need to either authenticate using something like
-Google auth, or start by resetting their passwords.
-
-You can use the `./manage.py send_password_reset_email` command to
-send password reset emails to your users.  We
-recommend starting with sending one to yourself for testing:
-
-```
-./manage.py send_password_reset_email -u username@example.com
-```
-
-and then once you're ready, you can email them to everyone using e.g.
-```
-./manage.py send_password_reset_email -r '' --all-users
-```
-
-(replace `''` with your subdomain if you're using one).
+{!import-login.md!}
 
 ## Caveats
 

templates/zerver/help/import-or-export-a-zulip-organization.md

@@ -78,25 +78,4 @@ cd /home/zulip/deployments/current
 ./manage reactivate_realm -r ''  # Reactivates the organization
 ```
 
-## Logging in
-
-Once the import completes, all your users will have accounts in your
-new Zulip organization, but those accounts won't have passwords yet
-(since for very good security reasons, passwords are not exported).
-Your users will need to either authenticate using something like
-Google auth, or start by resetting their passwords.
-
-You can use the `./manage.py send_password_reset_email` command to
-send password reset emails to your users.  We
-recommend starting with sending one to yourself for testing:
-
-```
-./manage.py send_password_reset_email -u username@example.com
-```
-
-and then once you're ready, you can email them to everyone using e.g.
-```
-./manage.py send_password_reset_email -r '' --all-users
-```
-
-(replace `''` with your subdomain if you're using one).
+{!import-login.md!}

templates/zerver/help/include/import-login.md

@@ -0,0 +1,22 @@
+## Logging in
+
+Once the import completes, all your users will have accounts in your
+new Zulip organization, but those accounts won't have passwords yet
+(since for very good security reasons, passwords are not exported).
+Your users will need to either authenticate using something like
+Google auth, or start by resetting their passwords.
+
+You can use the `./manage.py send_password_reset_email` command to
+send password reset emails to your users.  We
+recommend starting with sending one to yourself for testing:
+
+```
+./manage.py send_password_reset_email -u username@example.com
+```
+
+and then once you're ready, you can email them to everyone using e.g.
+```
+./manage.py send_password_reset_email -r '' --all-users
+```
+
+(replace `''` with your subdomain if you're using one).