Update dEQP/Cherry setup documentation
Update dEQP/Cherry setup documentation

Cherry now runs out of memory when using 32-bit Go. The 64-bit version
of Go requires a 64-bit version of GCC, which comes with MinGW-W64.
See also https://android.googlesource.com/platform/external/cherry/+/9592629522babac1fb1a337433ae27f78f696703/README#29

dEQP's Python scripts have been updated to require Python 3.

Bug: b/167692239
Change-Id: I6397f048420ba5b46199660166bb560182334c99
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/51108
Tested-by: Nicolas Capens <51edc787c30f24c4904e8ffbb5523c3a9f7a451d@google.com>
Reviewed-by: Alexis Hétu <1c7141772178a7e80858c3db5052b328076f08f4@google.com>
Kokoro-Result: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

google/swiftshader,bkaradzic/SwiftShader,bkaradzic/SwiftShader,google/swiftshader,bkaradzic/SwiftShader,google/swiftshader,bkaradzic/SwiftShader,bkaradzic/SwiftShader