doc: missing documentation

[crusso]

We still need more doc or one page tutorials for:

• [ ] numeric conversions (https://dfinity.slack.com/archives/CPL67E7MX/p1709150971197719)
• [ ] object combination (record extension)
• [ ] option blocks
• [ ] candid serialization (to_candid/from_candid)
• [ ] raw calls
• [ ] async*/await*
• [ ] actor class management
• [x] timers
• [x] randomness
• [ ] examples repo samples for the above
• [ ] management canister calls
• [x] playground
• [ ] FAQ
  • [x] overiding compiler version for dfx (DFX_MOC_PATH)
  • [x] proving compiler flags to dfx (args field of .json)
  • [x] using vessel/mops

[crusso]

@roman-kashitsyn suggests: it would be great to describe the do ? syntax in this article: https://internetcomputer.org/docs/current/motoko/main/errors