[SYCL][Doc] Add documentation about our releases (#17879)

Co-authored-by: Steffen Larsen <steffen.larsen@intel.com>

Author: AlexeySachkov

sycl/doc/Releases.md

@@ -0,0 +1,52 @@
+# Releases at intel/llvm
+
+intel/llvm provides a few ways for you to get SYCL compiler and this
+page is intended to document them as well as provide links and instructions
+how to you use them.
+
+## Nightly builds
+
+The project is being built and tested every night and those builds
+are published on GitHub as `nightly-YYYY-MM-DD` tags.
+
+Those builds are of **pre-release** quality: they are only suitable
+for early integration and testing of a bleeding-edge compiler.
+
+Because those builds are made from the latest commit available,
+there is no guarantee of any stability of those builds.
+
+Please note that those builds are tailored for our own testing needs
+and therefore they are built with assertions enabled and may have additional
+dependencies.
+
+## Official releases
+
+Official release branches are occasionally created to provide
+stable and validated commits for end users. The list below is
+ordered from the newest to the oldest.
+
+Release branches are prefixed with `sycl-rel-`
+
+### **[Upcoming]** `6.2.0` release
+
+This release will be made from
+the [`sycl-rel-6_2`](https://github.com/intel/llvm/tree/sycl-rel-6_2) branch.
+
+### `6.1.0` release
+
+This release was made from
+the [`sycl-rel-6_1_0`](https://github.com/intel/llvm/tree/sycl-rel-6_1_0)
+branch and we have the following tags published:
+- **[Latest]** [`v6.1.0`](https://github.com/intel/llvm/releases/tag/v6.1.0)
+
+### `6.0.X` releases
+
+These releases are made from
+the [`sycl-rel-6_0_0`](https://github.com/intel/llvm/tree/sycl-rel-6_0_0)
+branch and we have the following tags published:
+- [`v6.0.1`](https://github.com/intel/llvm/releases/tag/v6.0.1) -
+  6.0.1 bugfix release
+- [`v6.0.0`](https://github.com/intel/llvm/releases/tag/v6.0.0) -
+  6.0.0 release
+- [`v6.0.0-rc1`](https://github.com/intel/llvm/releases/tag/v6.0.0-rc1) -
+  release candidate 1 for 6.0.0 release

sycl/doc/index.rst

@@ -10,6 +10,7 @@ Using oneAPI DPC++ for Application Development
    GetStartedGuide
    Getting Started (Japanese) <https://www.isus.jp/others/get-started-with-oneapi-dpc/>
    UsersManual
+   Releases
    PreprocessorMacros
    cuda/contents
    Extensions <https://github.com/intel/llvm/tree/sycl/sycl/doc/extensions>