[zsh] Add warning when using zplug without gawk installed

.zsh/config/00_zplug.zsh

@@ -0,0 +1,10 @@
+#
+# zplug settings
+#
+
+if [ -n "${ZPLUG_HOME}" ] ; then
+    if ! command -v gawk >/dev/null 2>&1 ; then
+        printf "[zplug] warning: gawk is not installed\n"
+    fi
+fi
+