[doc] Update Xcode support policy (actions#10876)

README.md

@@ -122,7 +122,7 @@ The `-latest` migration process is gradual and happens over 1-2 months in order
 | .NET Core | 2 latest LTS versions and 1 latest version. For each feature version only latest patch is installed |
 | GCC <br/> GNU Fortran <br/> Clang <br/> GNU C++ | 3 latest major versions |
 | Android NDK | 1 latest non-LTS, 2 latest LTS versions |
-| Xcode     | - all OS compatible versions side-by-side <br/> - for beta, GM versions - latest beta only <br/> - old patch versions are deprecated in 3 months |
+| Xcode     | - only one major version of Xcode will be supported per macOS version <br/> - all minor versions of the supported major version will be available <br/> - beta and RC versions will be provided "as-is" in the latest available macOS image only no matter of beta/GA status of the image <br/> - when a new patch version is released, the previous patch version will be replaced |
 
 ### Package managers usage