Example charm encourages bad practices

https://juju.ubuntu.com/docs/authors-charm-writing.html encourages
some very bad practices, e.g.

| chmod -R 777 /var/www/vanilla/conf /var/www/vanilla/uploads /var/www/vanilla/cache

This makes these files writable by *any* user on the instance which is
not a good idea.

| wget "$dl" -O /tmp/vanilla.tar.gz

This is a security vulnerability as /tmp is a shared resource.

| cp /var/www/vanilla/conf/config.php /tmp/

id.

I appreciate this is an example charm and you probably don't want to
make it more complicated than necessary but I also feel we probably
shouldn't make it such that the first charm that a prospective charm
writer sees is full of dangerous practices like these.