Add gitignore and README for Vulkan deps.

.gitignore

Index: .gitignore
diff --git a/.gitignore b/.gitignore
index dc229236fa2cdd081c1edf3e08db29dfb1e5b644..8bf691f35c3a8b882408d9dc92559523c94999c9 100644
--- a/.gitignore
+++ b/.gitignore
@@ -350,6 +350,7 @@ vs-chromium-project.txt
 /third_party/freetype2/src
 /third_party/gles2_conform
 /third_party/glslang/src
+/third_party/glslang-angle/src
 /third_party/gnu_binutils/
 /third_party/google_appengine_cloudstorage
 /third_party/google_toolbox_for_mac/src
@@ -442,7 +443,9 @@ vs-chromium-project.txt
 /third_party/skia
 /third_party/smhasher/src
 /third_party/snappy/src
+/third_party/spirv-headers/src
 /third_party/SPIRV-Tools/src
+/third_party/spirv-tools-angle/src
 /third_party/sqlite4java/lib/**/*.dll
 /third_party/sqlite4java/lib/**/*.jar
 /third_party/sqlite4java/lib/**/*.jnilib
@@ -456,6 +459,7 @@ vs-chromium-project.txt
 /third_party/usrsctp/usrsctplib
 /third_party/v8-i18n
 /third_party/valgrind
+/third_party/vulkan-validation-layers/src
 /third_party/v4l2capture
 /third_party/visualmetrics
 /third_party/wayland/src