Add changelog for new metadata subcommand
All notable changes to [Solang](https://github.com/hyperledger/solang/)
will be documented here.
+## Unreleased
+
+### Added
+- Introduce new sub-command `solang idl` which can be used for generating
+ a Solidity interface file from an Anchor IDL file. This can be used for calling
+ Anchor Contracts on Solana. [seanyoung](https://github.com/seanyoung)
+
## v0.1.13 Genoa
### Changed
