Avoid OPcache errors (fixes #209)

conf/php-fpm.conf

@@ -433,7 +433,10 @@ env[PATH] = $PATH
 php_value[upload_max_filesize] = 10G
 php_value[post_max_size] = 10G
 php_value[default_charset] = UTF-8
-php_value[opcache.enable]=1
+; OPcache is already activated by default
+; php_value[opcache.enable]=1
+; The following parameters are nevertheless recommended for Nextcloud
+; see here: https://docs.nextcloud.com/server/15/admin_manual/installation/server_tuning.html#enable-php-opcache
 php_value[opcache.enable_cli]=1
 php_value[opcache.interned_strings_buffer]=8
 php_value[opcache.max_accelerated_files]=10000