Add Release.md (#5622)

Co-authored-by: Imbris <2002109+Imberflur@users.noreply.github.com>

RELEASE.md

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+This is an overview of how to run wgpu releases.
+
+## Structure
+
+We do a major breaking release every 12 weeks. This happens no matter the status of various in-flight projects.
+
+We do a patch releases as needed in the weeks between major releases. Once a new major release is cut, we stop doing patch releases for the previous major release unless there is a critical bug or a compilation issue.
+
+## People
+
+Anyone can perform most of these steps, except actually publishing the crates.
+
+Currently only @kvark and @cwfitzgerald can publish all crates. @grovesNL can also publish `wgpu` crates. @jimblandy can publish `naga` crates. @msiglreith can publish `d3d12`.
+
+## Major Release Process
+
+Approx 1 Week Before:
+- Determine if `glow` (@groves), `metal-rs` (@kvark and @cwfitzgerald) or any other dependant crates will need a release. If so, coordinate with their maintainers.
+- Go through the changelog:
+  - Re-categorize miscategorized items.
+  - Edit major changes so a user can easily understand what they need to do.
+  - Add missing major changes that users need to know about.
+  - Copy-edit the changelog for clarity.
+
+Day of Release:
+- Update all crates to be the new version. We bump all versions even if there were no changes.
+  - `d3d12`
+  - `naga`
+  - `naga-cli`
+  - `wgpu-types`
+  - `wgpu-hal`
+  - `wgpu-core`
+  - `Cargo.toml` (this covers the rest of the crates).
+- Ensure `glow` and `metal` are updated to the latest version if needed.
+- Add a new header for the changelog with the release version and date.
+- Create a PR with all of the version changes and changelog updates.
+- Once the PR is CI clean, (force) merge it.
+- Checkout `trunk` with the merged PR.
+- Publish! These commands can be pasted directly into your terminal in a single command, and they will publish everything.
+  ```bash
+    cargo publish -p d3d12
+    cargo publish -p naga
+    cargo publish -p naga-cli
+    cargo publish -p wgpu-types
+    cargo publish -p wgpu-hal --all-features
+    cargo publish -p wgpu-core --all-features
+    cargo publish -p wgpu
+    cargo publish -p wgpu-info
+  ```
+- Create a new release on the `wgpu` repo with the changelog and a tag called `vX.Y.Z`.
+- Create a branch with the with the new version `vX.Y` and push it to the repo.
+- Publish the link to the github release in the following places.
+  - [r/rust](https://www.reddit.com/r/rust/).
+    - Add an AMA comment.
+  - Crosspost to [r/rust_gamedev](https://www.reddit.com/r/rust_gamedev/).
+    - Add an AMA comment.
+  - Include the r/rust post shortlink in the following posts as well:
+  - [wgpu matrix](https://matrix.to/#/#wgpu:matrix.org)
+  - [Rust Gamedev Discord](https://discord.gg/yNtPTb2) in the #crates channel
+  - [Bevy Discord](https://discord.com/invite/bevy) in the #rendering-dev channel
+  - [Graphics Programming Discord](https://discord.gg/6mgNGk7) in the #webgpu channel
+  - [Rust Community Discord](https://discord.gg/rust-lang-community) in the #games-and-graphics channel
+- Complete the release's milestone on GitHub.
+- Create a new milestone for the next release, in 12 weeks time.
+
+## Patch Release Process
+- Enumerate all PRs that haven't been backported yet. These use the `needs-backport` label. [GH Link](https://github.com/gfx-rs/wgpu/issues?q=label%3A%22PR%3A+needs+back-porting)
+- On _your own branch_ based on the latest release branch. Cherry-pick the PRs that need to be backported. When modifying the commits, use --append to retain their original authorship.
+- Remove the `needs-backport` label from the PRs.
+- Fix the changelogs items and add a new header for the patch release with the release version and date.
+- Once all the PRs are cherry-picked, look at the diff between HEAD and the previous patch release. See what crates changed.
+- Bump all the versions of the crates that changed.
+- Create a PR with all of the version changes and changelog updates into the release branch.
+- Once the PR is CI clean, (force) rebase merge it.
+- Checkout the release branch with the merged PR.
+- Publish all relevant crates (see list above).
+- Create a new release on the `wgpu` repo with the changelog and a tag called `vX.Y.Z` on the release branch.
+- Backport the changelog and version bumps to the `trunk` branch.
+  - Ensure that any items in the newly-released changelog don't appear in the "unreleased" section of the trunk changelog.