Updated readme to recreate build on Arch and use Conda

I had trouble recreating the build as per the issue i opened. By making the changes listed (specifically removing PALISADEtrapdoor from CMakeLists.txt) I was able to build successfully and avoid the aforementioned issue

In the process I also added in build instructions for Arch Linux (minimal since Python3 is the default) and for using conda.

I ran the credit and simple datasets and achieved the same results for unencrypted and encrypted