Adjust cache_dir note

[wtmpx]

In this page: https://documentation.suse.com/suma/4.3/en/suse-manager/installation-and-upgrade/uyuni-install-requirements.html#server-hardware-requirements

we recommend minimme 100GB of /var/cache ; however, squid.conf have this configuration:

cache_dir aufs /var/cache/squid 15000 16 256

We have however a comment above this line advice customer to adjust the value to 60% of free space.

Size should be about 60% of your free space

I would vote to add a note in above page informing customers to adjust this value manually. A lot will not pay attention to squid.conf. This also should be added to our tune-guide.