ForgeGradle needs to generate and compile the Start classes what allows your IDE to run forge. But as it looks like the permissions on /home/hunar/Desktop/SpongeForge/build/tmp/makeStart/extracted/ are read only I guess.
Meaby offtopic and also a bit self promotion. If you are trying to get a debug environment working just for sponge you might want to try my plugin: https://forums.spongepowered.org/t/spongestart-gradle-plugin/ 
.