Feedback for the linux version of TB2 would be very appreciated, as it's practically untested right now. It does build and run, but that's all I have tested.
You need to compile it yourself. First you need to get the sources using git. Open the terminal and cd into some directory under which you want to have the sources. An example would be the ~/Documents directory. You do not need to create a sub directory for the sources, git will do this for you. Make sure you have git installed:
sudo apt-get install git
Then clone the sources:
git clone https://github.com/kduske/TrenchBroom.git
This will create a directory named "TrenchBroom" under your current directory, so if you did cd into ~/Documents, the sources will be in ~/Documents/TrenchBroom. cd into that directory.
Now you have to switch to the branch that contains the actual sources for TB2. You are currently on the master branch, which contains the TB1 sources.
git checkout develop
It should answer with a message such as this:
Branch develop set up to track remote branch develop from origin.
Switched to a new branch 'develop'
To ensure you're on the right branch, issue the "git status" command:
git status
It should answer with a message such as this:
On branch develop
Your branch is up-to-date with 'origin/develop'.
nothing to commit, working directory clean
Now read the build instructions in the Build.txt file and follow them. If you run into any problems, report back.