Add comprehensive PTP FAQ documentation for microcontrollers

[Copilot]

User requested general information about PTP (Precision Time Protocol) on microcontrollers in the context of the LAN865x driver.

Changes

• Added ptp_faq.md: 25 Q&A covering PTP fundamentals, hardware requirements, Linux PHC integration, accuracy considerations, and automotive/industrial use cases. Includes practical examples for configuration, testing, and debugging.

• Updated README.md: Added PTP documentation section linking to FAQ and existing implementation guide.

Key Topics Covered

• Hardware timestamping vs software timestamping (sub-microsecond vs millisecond precision)
• LAN865x PHC capabilities and register access
• Linux kernel integration (ptp_clock_info, IOCTLs, ptp4l usage)
• Automotive applications (IEEE 802.1AS/gPTP, TSN, ADAS sensor fusion)
• Accuracy factors (oscillator quality, network jitter, implementation overhead)
• Troubleshooting common issues

Example from FAQ:

# Enable hardware timestamping
hwstamp_ctl -i eth1 -t 1 -r 1

# Run PTP daemon with hardware timestamps
ptp4l -i eth1 -m -H

# Verify synchronization accuracy
ptp4l -i eth1 -m | grep "master offset"

Documentation written in German per user's language preference. Complements existing ptp_todo.md implementation guide.

Original prompt

Ich habe zunächst allgemeine fragen zu ptp auf mikrokontrollern

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