docs: explain LunarG is the source of truth for releases (#5627)

GitHub releases were just the exact same as the LunarG releases,
since the same commit were used for both.
For this reason, we don't think it brings any value, and will stop
publishing new releases on the GitHub page.

Signed-off-by: Nathan Gauër <brioche@google.com>

README.md

@@ -24,6 +24,13 @@ headers, and XML registry.
 
 ## Downloads
 
+The official releases for SPIRV-Tools can be found on LunarG's
+[SDK download page](https://vulkan.lunarg.com/sdk/home).
+
+For convenience, here are also links to the latest builds (HEAD).
+Those are untested automated builds. Those are not official releases, nor
+are guaranteed to work. Official releases builds are in the Vulkan SDK.
+
 <img alt="Linux" src="kokoro/img/linux.png" width="20px" height="20px" hspace="2px"/>[![Linux Build Status](https://storage.googleapis.com/spirv-tools/badges/build_status_linux_clang_release.svg)](https://storage.googleapis.com/spirv-tools/badges/build_link_linux_clang_release.html)
 <img alt="MacOS" src="kokoro/img/macos.png" width="20px" height="20px" hspace="2px"/>[![MacOS Build Status](https://storage.googleapis.com/spirv-tools/badges/build_status_macos_clang_release.svg)](https://storage.googleapis.com/spirv-tools/badges/build_link_macos_clang_release.html)
 <img alt="Windows" src="kokoro/img/windows.png" width="20px" height="20px" hspace="2px"/>[![Windows Build Status](https://storage.googleapis.com/spirv-tools/badges/build_status_windows_release.svg)](https://storage.googleapis.com/spirv-tools/badges/build_link_windows_vs2019_release.html)
@@ -49,17 +56,14 @@ version.  An API call reports the software version as a C-style string.
 
 ## Releases
 
-Some versions of SPIRV-Tools are tagged as stable releases (see
+The official releases for SPIRV-Tools can be found on LunarG's
-[tags](https://github.com/KhronosGroup/SPIRV-Tools/tags) on github).
+[SDK download page](https://vulkan.lunarg.com/sdk/home).
-These versions undergo extra testing.
+
-Releases are not directly related to releases (or versions) of
+You can find either the prebuilt, and QA tested binaries, or download the
-[SPIRV-Headers][spirv-headers].
+SDK Config, which lists the commits to use to build the release from scratch.
-Releases of SPIRV-Tools are tested against the version of SPIRV-Headers listed
+
-in the [DEPS](DEPS) file.
+GitHub releases are deprecated, and we will not publish new releases until
-The release generally uses the most recent compatible version of SPIRV-Headers
+further notice.
-available at the time of release.
-No version of SPIRV-Headers other than the one listed in the DEPS file is
-guaranteed to work with the SPIRV-Tools release.
 
 ## Supported features
 

docs/downloads.md

@@ -1,6 +1,22 @@
 # Downloads
 
-## Latest builds
+## Vulkan SDK
+
+The official releases for SPIRV-Tools can be found on LunarG's
+[SDK download page](https://vulkan.lunarg.com/sdk/home).
+The Vulkan SDK is updated approximately every six weeks.
+
+## Android NDK
+
+SPIRV-Tools host executables, and library sources are published as
+part of the [Android NDK](https://developer.android.com/ndk/downloads).
+
+## Automated builds
+
+For convenience, here are also links to the latest builds (HEAD).
+Those are untested automated builds. Those are not official releases, nor
+are guaranteed to work. Official releases builds are in the Android NDK or
+Vulkan SDK.
 
 Download the latest builds of the [main](https://github.com/KhronosGroup/SPIRV-Tools/tree/main) branch.
 
@@ -15,14 +31,3 @@ Download the latest builds of the [main](https://github.com/KhronosGroup/SPIRV-T
 | --- | --- | --- |
 | [MSVC 2017](https://storage.googleapis.com/spirv-tools/badges/build_link_windows_vs2017_debug.html) | [clang](https://storage.googleapis.com/spirv-tools/badges/build_link_linux_clang_debug.html) | [clang](https://storage.googleapis.com/spirv-tools/badges/build_link_macos_clang_debug.html) |
 | | [gcc](https://storage.googleapis.com/spirv-tools/badges/build_link_linux_gcc_debug.html) | |
-
-
-## Vulkan SDK
-
-SPIRV-Tools is published as part of the [LunarG Vulkan SDK](https://www.lunarg.com/vulkan-sdk/).
-The Vulkan SDK is updated approximately every six weeks.
-
-## Android NDK
-
-SPIRV-Tools host executables, and library sources are published as
-part of the [Android NDK](https://developer.android.com/ndk/downloads).