include oss installation instructions for ubuntu

Summary: I spent a good chunk of time installing eden on a fresh ubuntu vm from github, so I kept track of all of the packages that I needed to end up installing. users can install these before attempting to run the `build.sh` script in order to make sure all dependencies are there. Some of these manifested in non-obvious error messages. I'm sure as time goes on these dependencies might change a bit, but I think its a good starting point for anyone and should save a few hours of headache.

Reviewed By: chadaustin

Differential Revision: D22716112

fbshipit-source-id: 49232232a8707ef59c47487fdcc0cb41afc702e8

README.md

@@ -90,6 +90,9 @@ This build script will create an output directory outside of the repository
 where it will perform the build.  You can control this output directory
 location by passing a  `--scratch-path` argument to the build script.
 
+On Ubuntu, install the requirements in `requirements_ubuntu.txt`.  You will
+also need m4 and Rust installed.
+
 # Support
 
 EdenSCM is the primary source control system used at Facebook, and is used for

requirements_ubuntu.txt

@@ -0,0 +1,8 @@
+cmake
+g++
+build-essential
+libssl-dev
+make
+zlib1g-dev
+python3-distutils
+pkg-config