Update README.md (by @nii236)

README.md

@@ -104,8 +104,9 @@ by passing the `-DENABLE_GUI=OFF` flag to the cmake invocation.
 
 ### Building for Windows
 
-You will need the usual build tools, CMake, a Windows cross-compiler, and flatc.
-On a Debian derivative (e.g. Ubuntu) these can be installed with:
+Ubuntu will require 20.04 or above. Cross-compiling with WSL is also confirmed to work.
+
+You will need the usual build tools, CMake, a Windows cross-compiler, and flatc. On a Debian derivative (e.g. Ubuntu) these can be installed with:
 
     apt-get install git build-essential cmake mingw-w64 libflatbuffers-dev
 
@@ -115,16 +116,7 @@ Before building, check out the project and the necessary submodules:
     cd solvespace
     git submodule update --init
 
-After that, build 32-bit SolveSpace as following:
-
-    mkdir build
-    cd build
-    cmake .. -DCMAKE_TOOLCHAIN_FILE=../cmake/Toolchain-mingw32.cmake \
-             -DCMAKE_BUILD_TYPE=Release \
-             -DFLATC=$(which flatc)
-    make
-
-Or, build 64-bit SolveSpace as following:
+Build 64-bit SolveSpace with the following:
 
     mkdir build
     cd build