message: Update open source documentation to reflect new system requirements
  Summary: We have dropped Ubuntu 16.04 support. Now the oldest Ubuntu we support is 18.04.
diff: @@ -21,10 +21,10 @@ brew install boost jsoncpp
  ```
  ### Ubuntu/Debian (64-bit)
  -Base requirements are automake & libtool, GCC >= 5, Python >= 3.6 and Boost >= 1.71.0, as well as
  +Base requirements are automake & libtool, GCC >= 7, Python >= 3.6 and Boost >= 1.71.0, as well as
  development versions of `iberty`, `jemalloc`, `jsoncpp`, `lz4`, `lzma`, and `zlib`.
  -#### Ubuntu 16.04+, Debian 10(Buster)+
  -The minimum supported Ubntu version is 16.04. The minimum supported Debian version is 10.
  +#### Ubuntu 18.04+, Debian 10(Buster)+
  +The minimum supported Ubuntu version is 18.04. The minimum supported Debian version is 10.
  A [convenience script](https://github.com/facebook/redex/blob/master/setup_oss_toolchain.sh)
  will set up the build environment. This may include downloading Python 3.6 and Boost 1.71.0
  