Add Dockerfile for easier dev (#815)

Dockerfile

@@ -0,0 +1,15 @@
+# This dockerfile was created for development & testing purposes
+#
+# Build as:             docker build -t pwndbg .
+#
+# For testing use:      docker run --rm -it --cap-add=SYS_PTRACE pwndbg bash
+#
+# For development, mount the directory so the host changes are reflected into container:
+#   docker run -it --cap-add=SYS_PTRACE -v `pwd`:/pwndbg pwndbg bash
+#
+FROM ubuntu:20.04
+
+ADD . /pwndbg/
+RUN cd /pwndbg && DEBIAN_FRONTEND=noninteractive ./setup.sh
+RUN echo 'source /pwndbg/gdbinit.py' >> ~/.gdbinit.py
+