Replace github.com code links with cs.opensource.google
Replace github.com code links with cs.opensource.google

Bug: docs update
Change-Id: I0e0a596456d4c534adb6a8f57455d3cfb9cb65b9
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/47289
Kokoro-Result: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Tested-by: Nicolas Capens <51edc787c30f24c4904e8ffbb5523c3a9f7a451d@google.com>
Reviewed-by: Sean Risser <2d04e98eeaa433fb55534399ab3ab2c06fdf7967@google.com>
Reviewed-by: Nicolas Capens <51edc787c30f24c4904e8ffbb5523c3a9f7a451d@google.com>

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