Document build steps

Hi @lixun910!

Would it be possible to give some very brief instructions here on how you built the GeoDa Wasm module, just to get me started?

Was assuming this involves running Emscripten against `libgeoda`, but I wasn’t sure how to find the entry point to `libgeoda` in the `geoda` repo. Or maybe you used a different method altogether 😄

Thank you for helping kick this off!

Start by locating the libgeoda entry point in the geoda repository and reviewing how Emscripten is used to build the GeoDa Wasm module. Document the brief build steps, including the relevant entry point and commands, so another contributor can reproduce the module build.

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