[Doc] Add a release guide

ChangeLog

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+<day of week> <month> <day> 2024 <Author> <[email protected]>
+
+	* Version 0.1.0
+
+	This is the first release of Unified Memory Framework project.
+
+	...

RELEASE_STEPS.md

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+## UMF Release Steps
+
+This document contains all the steps required to make a new release of UMF.
+
+As a helper, we use in this guide these 2 variables:
+```bash
+  set $VERSION = new full version (e.g., 0.1.0-rc1) # -rc1 included just as an example
+  set $VER = new major+minor only version (e.g., 0.1)
+```
+
+**Note:**
+> Before doing the final release, it's recommended to prepare a pre-release version - a "release candidate"
+> (or "rc" in short). This requires adding, e.g., `-rc1` to the VERSION string. When all tests and checks
+> end properly, you can follow up with the final release. If any fix is required, it should be included in
+> another rc version (e.g., `-rc2`).
+
+At the moment, UMF releases are aligned with oneAPI releases - at least one UMF version
+will be released for a oneAPI release. Once all changes planned for UMF release are accepted,
+we follow the process (described in more detail below):
+
+1. Checkout the appropriate branch (`main` or "stable" `v$VER.x`).
+2. Make changes for the release.
+3. Create a new tag based on the latest commit - it takes the form
+  `v<major>.<minor>.<patch>` (e.g., `v0.1.0`).
+4. Push the tag and branch to the upstream.
+5. Create a new GitHub release using the tag created in the previous step.
+6. Update downstream projects to utilize the release tag. If any issues arise
+   from integration, apply any necessary hot fixes to `v$VER.x`
+   branch and go back to step 2 - to create a patch release. This step can also be tested
+   using `rc` version, potentially followed by another `rc` tag.
+
+## Make a release locally
+
+Do changes for a release:
+- Start of appropriate branch:
+  - For patch release, do it from a stable branch:
+    - `git checkout v$VER.x` (e.g., checkout `v0.1.x` if this is a `v0.1.1` patch)
+    - If previously we decided not to create such branch, create it now, based on the appropriate minor or major tag
+  - For major/minor release start from the `main` branch
+- Add an entry to ChangeLog, remember to change the day of the week in the release date
+  - For major releases mention API and ABI compatibility with the previous release
+- Update project's version in a few places:
+  - Set the new $VERSION in `project` function in the top-level `CMakeLists.txt`
+  - `release` variable in `scripts/docs_config/conf.py` (for docs)
+  - `UMF_VERSION` variable in `.github/workflows/basic.yml` (for installation test)
+- For major releases update ABI version in `.map` and `.def` files
+  - These files are defined for all public libraries (`libumf` and `proxy_lib`, at the moment)
+- Commit these changes and tag the release:
+  - `git commit -a -S -m "$VERSION release"`
+  - `git tag -a -s -m "Version $VERSION" v$VERSION`
+- For major/minor release:
+  - If stable branch for this release is required, create it:
+    - `git checkout -b v$VER.x`
+    - For some early versions (like `0.1.0`) we may omit creation of the branch
+
+## Publish changes
+
+As patch releases should be done on the stable branches, pushing tags and branches differ a little.
+
+For patch release:
+  - `git push upstream HEAD:v$VER.x v$VERSION` - push branch and tag
+
+For major/minor release:
+  - Push main:
+    - `git push upstream HEAD:main v$VERSION`
+  - And, if stable branch was also created, push it as well:
+    - `git checkout v$VER.x`
+    - `git push upstream HEAD:v$VER.x`
+
+## Announce release
+
+To make the release official:
+- Go to [GitHub's releases tab](https://github.com/oneapi-src/unified-memory-framework/releases/new):
+  - Tag version: `v$VERSION`, release title: UMF $VERSION, description: copy entry from ChangeLog and format it with no tabs and no characters limit in line
+  - Prior to version 1.0.0, check the *Set as a pre-release* tick box.
+- Announce the release, where needed
+
+## More information
+
+To assure the community that the release is a valid package from UMF maintainers, it's recommended to sign the release
+commit and the tag (`-S`/`-s` parameters in commands above). If you require to generate a GPG key follow
+[these steps](https://docs.github.com/en/authentication/managing-commit-signature-verification/generating-a-new-gpg-key).
+After that you'd also have to add this new key to your GitHub account - please do the steps in
+[this guide](https://docs.github.com/en/authentication/managing-commit-signature-verification/telling-git-about-your-signing-key).