Documentation on Arm64 system registers

General topics:

• arm64e-on-macos.md : Apple architectures arm64 and arm64e on macOS
• apple-m1-features.md : Arm features in the Apple M1 chip (and a comparison with M2)
• pac-format.md : Pointer Authentication Code format
• build-with-features.md : Building generic binaries with specialized instructions
• references.md : Reference documentation on the Arm64 architecture

Arm reference topics:

• features.md : A list of all optional or mandatory Arm features for A-Profile
• registers.md : A list of all system registers in Arm architecture for A-Profile
• registers-fields.md : Detailed bitfields of all system registers
• instructions.md : A list of all Arm instructions