Improve README

[kushti]

"Readme / Usage instructions for Swift-Bindings-Lib for Sigma-Rust is outdated and missing important steps for compiling of Rust code:
https://github.com/ergoplatform/sigma-rust/tree/develop/bindings/ergo-lib-ios
For example instructions contains very old Xcode version: 13, but current version is 15."

[imgruntw]

is there any updates for improved README here?

[rhuze-emryk]

Hi, I am taking a stab at this. I am new here.

[captainvredina]

Hi maintainers, I've opened PR #835 ("docs(iOS): Xcode 15 + iOS targets & build steps") to modernize the Swift/iOS README and address the missing Rust iOS targets. This should resolve the outdated instructions noted in this issue. Please review the changes and let me know if anything needs tweaking.

Claiming the Bounty – 50 SigUSD for this issue as per the bounty label. Thank you!