I just wanted to share the tool, which I use to send my webmentions. I use the webmention Go library by Will Norris, which also includes a simple command line tool.
If you have Go installed on your computer, you can simply install it by typing this into your terminal:
go get willnorris.com/go/webmention/cmd/webmention
After that, just use the command
webmention followed by your post URL and you can select to which detected links it should try to send a webmention.
Have fun sending some!