Update private testnet doc

[abitmore]

The default value of required-participation parameter in witness plugin is 33, with this number, when starting a private testnet, the node won't produce blocks.

[cedar-book]

===============================================
-witness plugin options
===============================================
Enable block production, even if the chain is stale.
-enable-stale-production = false
Percent of witnesses (0-100) that must be participating in order to produce blocks
-required-participation = 33
ID of witness controlled by this node (e.g. "1.6.5", quotes are required, may specify multiple times)
-witness-id =
Tuple of [PublicKey, WIF private key] (may specify multiple times)
-private-key = .....
//---------- (the above is from current config.ini)----------------

Why the default value is 33?

What would be a recommendation for people who want to start a private testnet?

• enable-stale-production = false
• required-participation = 33 -->1? Can they start with 0 first time?
  //-----------------

Currently, Private Testnet - setup section says this. And Note: It’s important to activate a 2/3 majority of the witnesses defined in the genesis file.
If so, required-participation would depend on how many witnesses have been activated in thrie private testnet genesis file ?

[abitmore]

Yes, need to change required-participation to 0.

[cedar-book]

As a quick note. Updated the information on this page's example Configuration for Private Testnets and added a warning.

[oxarbitrage]

Added to https://github.com/bitshares/bitshares-core/wiki/private-testnet#starting-block-production

[abitmore]

Thank you.