Get rid of hardcoded ESD key in global/shopware.con

[bcremer]

After merging PR #8 I was thinking about creating a variable for the esd key to get rid of the hardcoded value in global/shopware.con.

# sites-available/example.com.conf
set $shopware_esd_key '552211cce724117c3178e3d22bec532ec';`

# global/shopware.con
location ^~ /files/$shopware_esd_key/ {
    internal;
}

Unfortunately that seems not possible with plain Nginx config.

[samuelvogel]

Maybe it should be documented that this part actually is the ESD key from the Shopware config as a first step!