add subaccount types

pages/api_integration-guides/how_to_transfer.md

@@ -1,6 +1,33 @@
 # How to transfer
 
-## Different account types
+## Account types
+
+**Main Account**
+* Otherwise known as your wallet/address account.
+* This account holds assets that are sent to/from the chain, including assets used for gas and collateral.
+* Gas for transactions is used from the main account.
+* Main accounts cannot not trade.
+
+**Subaccount**
+* Subaccounts are used to trade.
+* Each main account can have many subaccounts.
+* Each subaccount is uniquely identified using `(main account address, integer)`
+* Only the main account can send transactions on behalf of a subaccount.
+* Subaccounts do not require gas to trade (they will use the main account's gas).
+* Subaccounts require collateral token (currently USDC) in order to trade.
+
+## Subaccount types
+
+**Cross-margin Subaccount**
+* Cross-margin subaccounts are able to trade positions for all cross markets.
+* Cross-margin subaccounts share a single collateral pool for all positions.
+* Cross-margin subaccounts are not able to trade isolated markets.
+* Frontends (Web, Mobile) will use subaccount number `0` for all cross-margin trading.
+
+**Isolated Subaccount**
+* Isolated subaccounts are able to trade positions for single isolated market at a time.
+* Isolated subaccounts are not able to trade cross markets.
+* Frontends (Web, Mobile) will use subaccount numbers `TODO` for isolated market trading.
 
 ## Transfer from main account to subaccounts
 Use deposit transaction