docs: notes on submitting winpkg update

Author: jaromil

build/README_WINPKG.md

@@ -0,0 +1,19 @@
+# Instructions to submit a new release to winpkg
+
+Download the latest `CJIT_installer.exe` and note the version.
+
+Run `./build/winpkg-update.sh` with `CJIT_installer.exe` as file and version string.
+
+This will generate the new manifest in `manifest/`.
+
+Then validate the manifest:
+
+```
+winget validate --manifest manifests/d/Dyne/CJIT/X.X.X/
+```
+
+Then use wingetcreate to submit the update:
+
+```
+wingetcreate submit --prtitle "New Version: Dyne.CJIT version X.X.X" manifests/d/Dyne/CJIT/X.X.X/
+```