Imagemagick - Docker mod for nginx/letsencrypt

This mod adds imagemagick and the php7 imagick module to nginx/letsencrypt, to be installed/updated during container start.

In nginx/letsencrypt docker arguments, set an environment variable DOCKER_MODS=linuxserver/mods:letsencrypt-imagemagick

If adding multiple mods, enter them in an array separated by |, such as DOCKER_MODS=linuxserver/mods:letsencrypt-imagemagick|linuxserver/mods:letsencrypt-mod2