To build the AppImage, you basically just have to:

1. Build the base docker image

docker pull centos:6.10
docker build <path/to/this_directory_containing_the_Dockerfile>

Building the image will take several hours at least.

2. Create a container from image and open a shell

docker images (should show the image ID of the newly created image)
docker run -t -i --name kdevelopappimagecreator <image id>

3. Copy the script and patches into the docker container

docker cp kdevelop-recipe-centos6.sh kdevelopappimagecreator:/
for p in *.patch ; do docker cp $p kdevelopappimagecreator:/ ; done

4. Run the script in the interactive shell of the container

./kdevelop-recipe-centos6.sh

Running the script will also take quite a while the first time you do it, so it is advisable to always re-use the same container.

5. Copy the resulting AppImage out of the container

docker cp kdevelopappimagecreator:/out/KDevelop-git-x86_64.AppImage .