add docs

Signed-off-by: Jason Hall <[email protected]>

docs/features/wasm.md

@@ -0,0 +1,30 @@
+# Wasm
+
+`ko` has early **experimental** support for building wasm containers.
+
+This currently requrires:
+
+- `ko` built from head (`go install github.com/google/ko@main`)
+- [Go 1.21](https://go.dev/dl/) or later
+- [up-to-date Docker Desktop with experimental features enabled](https://docs.docker.com/desktop/wasm/)
+
+With those requirements met, you can build a wasm container with:
+
+```sh
+ko build ./cmd/app --platform=wasip1/wasm
+```
+
+You can then run this image with:
+
+```sh
+docker run \
+  --runtime=io.containerd.wasmedge.v1 \
+  --platform=wasip1/wasm \
+  ${IMAGE}
+```
+
+### Known Limitations
+
+- SBOMs are not generated for containers built this way
+- `--platform` must only specify `wasip1/wasm`, and no other platforms
+- Test coverage is limited. [Anecdotally](https://github.com/ko-build/ko/pull/1095), the `wasmedge` and `wasmtime` runtimes should work, but `slight` and `spin` do not currently.