"Browser Usage" in Readme probably wrong due to synchronous webassembly compilation

[ekpyron]

We specifically compile soljson.js with WASM_ASYNC_COMPILATION=0 - there was a reason for this, but I don't remember right now.
However, I think at least chromium-based browsers won't allow synchronous compilation from the main thread. This effectively means that loading the compiler has to be done from web workers right now (at least if it's supposed to work in all browsers) and the "Browser Usage" section in README.md is outdated.

So we need to check if we can switch to asynchronous compilation in solidity, investigate if and what kind of problems synchronous compilation entails and adjust the section in the readme accordingly.

[jhubbardsf]

Any updates on this? Still getting a compiler error when trying to load it in browser (chromium based).