Make it easier to follow cmake/README.md instructions
When following the instructions directly (for developing on Windows) we should end up with a generator that's easy to run for csharp/generate_protos.sh, and we shouldn't end up trying to stage the build output.
diff --git a/.gitignore b/.gitignore
index 8afb522..8b76496 100644
--- a/.gitignore
+++ b/.gitignore
@@ -89,6 +89,10 @@
# Windows native output.
cmake/build
build_msvc
+# Directories suggested by cmake/README.md
+/debug/
+/solution/
+/release/
# NuGet packages: we want the repository configuration, but not the
# packages themselves.
