README: initial readme

Signed-off-by: Stephen Gutekanst <stephen@hexops.com>

README.md

@@ -0,0 +1,32 @@
+# vulkan-headers packaged for the Zig build system
+
+This is a fork of [vulkan-headers](https://github.com/KhronosGroup/Vulkan-Headers), packaged for Zig. Unnecessary files have been deleted, and the build system has been replaced with build.zig.
+
+## Updating
+
+To update this repository, we run the following:
+
+```sh
+git remote add upstream https://github.com/KhronosGroup/Vulkan-Headers || true
+git fetch upstream
+git merge upstream/main --strategy ours
+```
+
+## Verifying repository contents
+
+For supply chain security reasons (e.g. to confirm we made no patches to the code) you can verify the contents of this repository by adding the upstream version as a remote:
+
+```sh
+git remote add upstream https://github.com/KhronosGroup/Vulkan-Headers || true
+git fetch upstream
+```
+
+And then comparing using `git diff` with some options to _exclude deleted files_, and exclude `README.md`, `build.zig`, and `.gitignore` from the diff:
+
+```sh
+git diff $(git merge-base origin/main upstream/main)..origin/main \
+    --diff-filter=d \
+    ':(exclude)README.md' \
+    ':(exclude)build.zig' \
+    ':(exclude).gitignore'
+```