[Solr] Refuse to start with RAM lt 2 GB

[Config/Update] Set limits and change descriptions for Solr

update.sh

@@ -219,6 +219,7 @@ for option in ${CONFIG_ARRAY[@]}; do
       echo "Adding new option \"${option}\" to mailcow.conf"
       echo '# Solr heap size, there is no recommendation, please see Solr docs.' >> mailcow.conf
       echo '# Solr is a prone to run OOM on large systems and should be monitored. Unmonitored Solr setups are not recommended.' >> mailcow.conf
+      echo '# Solr will refuse to start with total system memory below or equal to 2 GB.' >> mailcow.conf
       echo "SOLR_HEAP=1024" >> mailcow.conf
   fi
   elif ! grep -q ${option} mailcow.conf; then