It is very easy to type “special” characters on Linux (i.e. those that aren’t printed on the keyboard). It’s called the Compose or Multi Key, and it’s brilliant.
First, enable it in ‘Keyboard settings > Advanced > Position of Compose Key’. I’ve got it set to Left <a href="https://en.wikipedia.org/wiki/Windows_key%22>Win</a> because I never use that for anything and it’s in a similar position to the key on Apple computers that serves a similar purpose (but whose name I cannot remember).
If the Left Win option is missing (as it seems to be on some Ubuntu installations), you just need to edit /etc/default/keyboard and set:
XKBOPTIONS="compose:lwin"
Then run:
sudo dpkg-reconfigure keyboard-configuration
Once it’s all working you just need to look up the characters you want (Tim Starling also has a good list).