message: Update pgsql documentation regard wallet_scheme
diff: @@ -75,19 +75,28 @@ cd indy-sdk/experimental/plugins/postgres_storage
  RUST_BACKTRACE=1 cargo test -- --nocapture --test-threads=1
  ```
  -## Database-per-wallet vs Multi-wallet database
  -
  -The plug-in supports two schemes - a database per wallet, or a single database containing multiple wallets.
  -
  -Note to use the multi-wallet-database mode you need to call an initial init() function in the plug-in.
  -
  -In the initial wallet config:
  +## Wallet management modes
  +The plug-in supports three modes
  +- `DatabasePerWallet` - each wallet has its own database
  +- `MultiWalletSingleTable` - all wallets are stored in single table in single database. Each wallet has its own
  +connection pool.
  +- `MultiWalletSingleTableSharedPool` - all wallets are stored in single table in single database. The plugin
  +will create only 1 connection pool reused by all wallets. This can be useful if intend to open many different
  +wallets. Postgres has by default limitation of ~100 simultaneous connections and using this strategy you can
  +limit number of DB connections significantly.
  +
  +By default is used `DatabasePerWallet` mode, however you can override this by specifying
  +value of `wallet_scheme` with value `MultiWalletSingleTable` or `MultiWalletSingleTableSharedPool`.
  +The wallet configuration must be passed into external function
  + `init_storagetype(config, credentials)` when using pgsql as plugin from external code.
  +
  +Here's sample wallet configuration which will initialize plugin to use `MultiWalletSingleTable` strategy.
  ```
  {"url":"localhost:5432", "wallet_scheme":"MultiWalletSingleTable"}
  ```
  -The default if not specified is database-per-wallet.
  +If `wallet_scheme` is not defined in wallet configuration, `DatabasePerWallet` scheme is used by default.
  To run unit tests in each mode, specify:
  