Installation:
a) Extract to \.minecraft\versions
b) Rename folder to 'Advanced Darkness'
c) Copy a 1.6.2 jar from \.minecraft\versions\1.6.2 to \.minecraft\versions\Advanced Darkness (the folder you just renamed!)
d) Rename "1.6.2.jar" to "Advanced Darkness.jar"
e) Inject classes from \client\classes into "Advanced Darkness.jar", and delete the META-INF folder
f) Open the new launcher (Yggdrasil), create/edit a profile, select 'release Advanced Darkness'.
g) Launch! If you did it right, it should launch perfectly.

If 1.6.2 is not the latest version of the mod, replace 1.6.2 in all file names to the newest version. This may be an oversight of me not updating the readme.

ex. 1.7 is released and I update AD as noted from the forum topic. The readme still says 1.6.2. Copy 1.7 folders instead of 1.6.2.