add the desc of proposals only support voting for yes

Author: abn2357

docs/using_javatron/private_network.md

@@ -93,7 +93,7 @@ The process of building a node on private chain is the same as that on mainnet.
       ```
     
     * Proposal  
-      Any witness(SR, SR partner, SR candidate) is entitled to create a proposal, SRs also have the right to vote for the proposal. A witness uses [proposalcreate](https://developers.tron.network/reference/proposalcreate) to create a proposal, and then SRs use [proposalapprove](https://developers.tron.network/reference/proposalapprove) to approve the proposal. Below is an code example of modifying two dynamic parameters through a committee proposal. In [proposalcreate](https://developers.tron.network/reference/proposalcreate), dynamic parameters are represented by numbers, the mapping between number and string name of dynamic parameters can be seen [here](https://developers.tron.network/reference/wallet-getchainparameters).
+      Any witness(SR, SR partner, SR candidate) is entitled to create a proposal, SRs also have the right to vote for the proposal. A witness uses [proposalcreate](https://developers.tron.network/reference/proposalcreate) to create a proposal, and then SRs use [proposalapprove](https://developers.tron.network/reference/proposalapprove) to approve the proposal(Proposals only support voting for yes, super representatives do not vote means they do not agree with the proposal). Below is an code example of modifying two dynamic parameters through a committee proposal. In [proposalcreate](https://developers.tron.network/reference/proposalcreate), dynamic parameters are represented by numbers, the mapping between number and string name of dynamic parameters can be seen [here](https://developers.tron.network/reference/wallet-getchainparameters).
       ```
       var TronWeb = require('tronweb');
       var tronWeb = new TronWeb({