Code:
cd
rm -Rf watchdog_pi/
git clone git://github.com/seandepagnier/watchdog_pi.git
cd watchdog_pi/
mkdir build
mv src/WatchdogUI.h include/
cd build
cmake ..
make
sudo make install
This should work on a raspberry and the whole sequence can be repeated if needed. After this, restart OpenCPN and the plugin should be available. Note that one file needed to be moved for the compile to work. This is bound to be solved soon, but it won't affect the install script.