glassfish: add README

plugins/glassfish/README.md

+# glassfish
+
+The glassfish plugin adds completion for the `asadmin` utility, a command to manage
+[Oracle GlassFish](https://docs.oracle.com/cd/E18930_01/html/821-2416/giobi.html) servers.
+
+To use it, add `glassfish` to the plugins array in your zshrc file:
+```zsh
+plugins=(... glassfish)
+```

plugins/glassfish/glassfish.plugin.zsh

-# if there is a user named 'glassfish' on the system, we'll assume
-# that is the user asadmin should be run as
-# grep -e '^glassfish' /etc/passwd > /dev/null && alias asadmin='sudo -u glassfish asadmin'
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