5419 update check packages2install

... and create docs subfolder

docs/20_Checks/_index.md

+# Checks
+
+## Shared functions
+
+There is one include script used by all checks:
+[inc_pluginfunctions](inc_pluginfunctions.md)
+
+## Check scripts
+
+* check_apache_requests
+* check_backup_one
+* check_ceph_diskfree
+* check_ceph_osd
+* check_ceph_status
+* check_clientbackup
+* check_couchdb-lb
+* [check_cpu](check_cpu.md)
+* check_cronstatus
+* check_disk-io
+* check_dns_responsetime
+* [check_eol](check_eol.md)
+* check_haproxy_health
+* check_haproxy_status
+* check_memory
+* check_netio
+* check_netstat
+* check_opencpu
+* check_packages2install
+* check_proc_mem
+* check_proc_ressources
+* check_proc_zombie
+* check_reboot_required
+* check_sensuplugins
+* check_smartstatus
+* [check_snmp_data](check_snmp_data.md)
+* check_snmp_synology
+* check_ssl
+* check_systemdservices
+* check_timesync
+* check_uptime
+* hello