Fixed 'add user command' in Admin Web Services

Fixes #1480

Author: ForgottenProgramme

src/maintainer/infrastructure.rst

@@ -154,7 +154,7 @@ merge the PR into a separate branch on your feedstock if you want to keep these
 other builds. **Python 2.7 support is deprecated and any feedstocks on Python 2.7 will
 not be properly handled by our bots.**
 
-@conda-forge-admin, please add <@user>
+@conda-forge-admin, please add user <@username>
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 Entering the above phrase in the title of an issue on a feedstock will make a PR