"How can setup my multisite installation with several domains?"
--> "Do you have multisite installed in /public_html?
I see every thread for this plugin (for the last 3-4 years) and do not recall any where someone responded with public_html. The public_html folder is typical of web accounts created with cPanel but I do not know of any other control panels that use it.
"No it's installed in /wp/
--> "Then you can't map domains, at least not with this plugin."
You can use domain mapping when WP is installed in a folder as long as the home of the main site is in the root. That change is effective WP 3.4 or 3.5.
There's a lot of info on that page
Agreed. The home has to be in the root of the website is a limitation of the way http/web browsers work. The DM plugin doesn't support it because it does not otherwise work.
Adding the note probably would eliminate some threads. However those would be replaced with people asking to have the feature added and/or asking why the plugin doesn't support it.
IOW, we would be trading thread subjects from folks who are not familiar with the limitations of http/web browsers.