chore: update Readme; rm rlib; strip libraries

[markphelps]

s- small readme update

• dont build rlib (Rust shared library) for now see: Simple dylib linking fails. rust-lang/rust#19680
• strip dlls of build/debug symbols for smaller size

Saves about 2MB on MacOS, havent tried on linux yet

-rw-r--r--  1 markphelps  staff   780B Dec 26 19:30 libfliptengine.d
-rwxr-xr-x  1 markphelps  staff    10M Dec 26 19:30 libfliptengine.dylib
workspace/client-sdks - [readme-rlib●] » strip -x flipt-client-ruby/lib/ext/darwin_arm64/libfliptengine.dylib
workspace/client-sdks - [readme-rlib●] » ls -lah flipt-client-ruby/lib/ext/darwin_arm64/
total 17024
drwxr-xr-x  4 markphelps  staff   128B Dec 26 19:30 .
drwxr-xr-x  4 markphelps  staff   128B Dec 26 19:27 ..
-rw-r--r--  1 markphelps  staff   780B Dec 26 19:30 libfliptengine.d
-rwxr-xr-x  1 markphelps  staff   8.3M Dec 26 19:30 libfliptengine.dylib