Clarify build instructions in the readme

[lrq3000]

There are missing build instructions, we need to build libraries first:

cd beautyxt_rs_typst
cargo build --lib --release --target aarch64-linux-android
copy .\target\aarch64-linux-android\release\libbeautyxt_rs_typst.so ..\app\src\main\jniLibs\arm64-v8a\libbeautyxt_rs_typst.so

cd beautyxt_rs_plain_text_and_markdown
cargo build --lib --release --target aarch64-linux-android
copy .\target\aarch64-linux-android\release\libbeautyxt_rs_plain_text_and_markdown.so ..\app\src\main\jniLibs\arm64-v8a\libbeautyxt_rs_plain_text_and_markdown.so

There are also two more necessary libraries that I don't know how to make: libdatastore_shared_counter.so and libjnidispatch.so

But anyway these libraries cannot be built on Windows because need clang to cross-compile and there are big issues to do that in Rust: https://github.com/rust-lang/cc-rs/issues/308

I found instructions to try to workaround this issue but they were too complicated and uncertain for the time I had to work on this.

So I just extracted the libs folder from the latest BeautyXT .apk and moved it to the expected path (app/src/main/ and renamed to jniLibs).

[soupslurpr]

Oh there are some build instructions for the Rust libraries in "useful-commands.txt" in the Rust library root folder. CONTRIBUTING.md talks about them. I'm on Windows 11 so it should hopefully work fine for you as well.

[lrq3000]

Oh ok sorry I missed that, usually CONTRIBUTING.md is more about how to open new issues and PRs. I'd suggest to clarify that in the readme (just mentioning that CONTRIBUTING also points to build instructions).

[soupslurpr]

alright done! Thanks for the suggestion.