fix: Change description of temporary limitations (#69)

* Change description of temporary limitations

* Update temp-limits.md

* Update temp-limits.md

docs/dev/zksync-v2/temp-limits.md

@@ -2,7 +2,7 @@
 
 ::: tip Call for feedback
 
-As we add new features, this page is constantly updated. Most of the issues listed here (especially around the opcodes) will be resolved by the time of the mainnet launch.  
+As we add new features, this page is constantly updated.
 
 If any of these block you, let us know on our [discord](https://discord.gg/px2aR7w), so we can prioritize accordingly.
 
@@ -16,7 +16,13 @@ However, if a library contains at least one `public` or `external` method, it is
 
 ## Unsupported opcodes
 
-#### Returning constant value
+- `SELFDESTRUCT` (it’s considered harmful and there are calls to deactivate it on L1).
+- `EXTCODECOPY` (it can be implemented if needed, but we skip it for now because zkEVM opcodes are not identical to EVM ones anyway).
+- `CALLCODE` (deprecated on Ethereum in favor of `DELEGATECALL`).
+
+## Temporarily simulated by constant values
+
+These opcodes will be supported by the time of the mainnet launch.
 
 - `block.gaslimit` always returns `2^32-1`.
 - `MSIZE` always returns `2^16`.
@@ -25,12 +31,9 @@ However, if a library contains at least one `public` or `external` method, it is
 - `GASPRICE` (`tx.gasprice`) always returns `0`.
 - `CHAINID` (`chain_id`) always returns `0`.
 - `BLOCKHASH` (`tx.blockhash`) always returns `0`.
-- `DIFFICULTY` (`block.difficulty`) always returns `0`.
-- `PC` always returns `0`.
 - `COINBASE` (`block.coinbase`) always returns `0`.
 
-#### NOOP
+## Ignored by the compiler
 
-- `EXTCODECOPY`
-- `SELFDESTRUCT` (`selfdestruct(addr)`)
-- `CALLCODE` (`callcode`)
+- `DIFFICULTY` (`block.difficulty`) always returns `0` (zkSync does not have proof of work consensus).
+- `PC` always returns `0` (we can technically support it, but most likely its use-cases are very specific for the EVM, so to avoid confusion it was decided not to; also, since solidity 0.7.0, it is non-accessible in yul and solidity).