Fix staking requirements

[matevz]

A user on discord asked about staking requirements for running compute Sapphire node. The current ParaTime staking values here https://docs.oasis.io/node/run-your-node/prerequisites/stake-requirements are not correct.

• Sapphire and Emerald compute requirement is 5,000,100 ROSE on Mainnet
• Mention how Oasis CLI can be used to show you the current ParaTime-level staking requirements (oasis net show native-token plus oasis net show paratimes) (docs: Add Oasis CLI commands to stake requirements #1022)
• Explain what do specific thresholds here mean. (Add oasis paratime show parameters to show ROFL staking thresholds cli#318)