Well, you can do it that way, but if you are not into compiling software or just want the easiest possible method, go to
https://tvheadend.org/projects/tvheadend/wiki/AptRepository and follow the instructions, but read the whole page before you do anything - you may prefer to use one of the "unofficial repositories" shown about halfway down the page. If you use one of those, installation is far easier, though you do lose the ability to compile in specific options. If you have no idea why you'd want to do that, then just stick with the repositories. If you want the latest and greatest, use the "unstable" version (which really isn't all that unstable, but be aware that upgrades potentially could break things, though that rarely happens).