add readme + patcher script for issue with iOS cross-compilation

barretenberg/bb_rs/README.md

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+# bb.rs
+
+Rust bindings for Barretenberg C++ codebase.
+
+## Build
+
+```
+# Build on your own machine
+cargo build -vvvv
+
+# Cross-compile for iOS
+cargo build -vvvv --target aarch64-apple-ios
+
+# Cross-compile for Android
+cargo build -vvvv --target aarch64-linux-android
+```
+
+## Known issues
+
+### Missing `sys/random.h`
+
+random.h is not available in the iOS SDK includes but it is available in the MacOS SDK includes. So you can copy it from `/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/sys` and paste it in `/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/usr/include/sys`. This will work, no compability issues, it's just not there for some reason.
+
+You can also run `scripts/patcher.sh` to do this (you may need to run it as `sudo`).
+
+
+

barretenberg/bb_rs/scripts/patcher.sh

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+# Fix some issues that can only be fixed manually
+
+# Copy random.h from MacOS to iOS
+cp /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/sys/random.h /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/usr/include/sys/random.h