Readme.md: Change way of cloning edk2 repo
UefiCpuPkg/CpuExceptionHandlerLib: always clear descriptor data in advance
MdeModulePkg: introduce UEFI freed-memory guard bit in HeapGuard PCD
MdeModulePkg: cleanup Heap Guard pool/page type PCD documentation
UefiCpuPkg/CpuDxe: prevent recursive calling of InitializePageTablePool
UefiCpuPkg/CpuDxe: consider freed-memory guard in non-stop mode
MdeModulePkg/Core: add freed-memory guard feature
MdeModulePkg/Core: prevent re-acquire GCD memory lock