Add references to interop materials

[unnawut]

Coordination

• pqinterop: https://github.com/leanEthereum/pm/blob/main/breakout-rooms/leanConsensus/pq-interop/pq-interop-pm.md
• leanmetrics: https://github.com/leanEthereum/pm/tree/main/breakout-rooms/leanMetrics

We should also list all relevant repositories, and make them very visible:

• https://github.com/leanEthereum/leanSpec
• https://github.com/leanEthereum/leanMultisig
• https://github.com/leanEthereum/leanMetrics

Client repos will be nice too

• https://github.com/ReamLabs/ream
• https://github.com/blockblaz/zeam
• https://github.com/qdrvm/qlean-mini