Add apex help_content for certs,nginx,storage,tar plugins

Also corrects some punctuation in associated help_content.

plugins/tar/commands

@@ -7,8 +7,9 @@ case "$1" in
     help_content_func () {
       declare desc="return tar plugin help content"
       cat<<help_content
+    tar, An alternative to using git. Apps are loaded via tarballs instead
     tar:in <app>, Reads an tarball containing the app from stdin
-    tar:from <app> <url>, Loads an app tarball from url.
+    tar:from <app> <url>, Loads an app tarball from url
 help_content
     }