make-install-script: add guide for top_dir argument

[daipom]

We need to specify top_dir as an argument, but it is unclear now.

Before

$ ruby make-install-script.rb --help
Usage: make-install-script [options]
    -a, --archive                    Enable archived installed script to verify with
    -b, --backup                     Backup original install script (e.g. https://toolbelt.treasuredata.com)
    -c, --channel TARGET_CHANNEL     Specify channel with comma separated (e.g. --channel 4,5)
    -d, --debug                      Enable debug logging
    -s, --site URL                   Specify distribution site (e.g. https://fluentd.cdn.cncf.io)
    -v, --verify                     Enable verification mode

After

$ ruby make-install-script.rb --help
Usage: ruby make-install-script.rb [options] top-dir
    -a, --archive                    Enable archived installed script to verify with
    -b, --backup                     Backup original install script (e.g. https://toolbelt.treasuredata.com)
    -c, --channel TARGET_CHANNEL     Specify channel with comma separated (e.g. --channel 4,5)
    -d, --debug                      Enable debug logging
    -s, --site URL                   Specify distribution site (e.g. https://fluentd.cdn.cncf.io)
    -v, --verify                     Enable verification mode

[kenhys]

Another idea: by default, assume top directory was specified.

diff --git a/make-install-script.rb b/make-install-script.rb
index dd1c113..b36e5fe 100644
--- a/make-install-script.rb
+++ b/make-install-script.rb
@@ -38,9 +38,8 @@ opt.on("-s", "--site URL", "Specify distribution site (e.g. https://fluentd.cdn.
 opt.on("-v", "--verify", "Enable verification mode") { options[:verify] = true }
 top_dir = opt.parse!(ARGV).first
 
-unless File.exist?(top_dir)
-  puts "#{top_dir} not found"
-  exit 1
+unless top_dir
+  top_dir = File.dirname(File.expand_path(__FILE__))
 end
 
 class FluentInstallScript

[daipom]

I see! Looks good!

[daipom]

Okay, let's go with that approach.
I close this PR now.