user guide: explain node syncing

[tzemanovic]

In https://docs.anoma.net/user-guide/ledger.html or somewhere around there, we should explain that unsynced node can be used to broadcast transactions, but the client won't be able to see transaction result until the node is synced to the height at which the transaction is applied (which usually results in timeout error: Encountered error while broadcasting transaction: Connection timed out).

We have a related issue to improve node logs to make it easier to see sync status in the node namada-net/namada#25, until then it's possible to use e.g. curl http://localhost:26657/status to check the sync status via tendermint

[tzemanovic]

I've also opened namada-net/namada#94 to have something nicer than curl http://localhost:26657/status

[cwgoes]

@bengtlofgren can you take this on?