howto: add event manager

add groups section in the getting started guide.
Suggest to prefer configuration with env vars instead of modifying
the default configuration file

Signed-off-by: Nicola Murino <nicola.murino@gmail.com>

pkgs/build.sh

@@ -1,6 +1,6 @@
 #!/bin/bash
 
-NFPM_VERSION=2.19.2
+NFPM_VERSION=2.20.0
 NFPM_ARCH=${NFPM_ARCH:-amd64}
 if [ -z ${SFTPGO_VERSION} ]
 then