WebAssembly: add WASIP1 runtime configuration examples

[iamrajiv]

This change adds a "WASIP1 Runtime Configuration" section to the
WebAssembly page.

It provides configuration examples for Wasmtime, Wazero, and Node.js
to properly map the host directory to the guest root / and set PWD.

Without this configuration, Go programs compiled for wasip1 often
fail with "Bad file number" errors instead of the expected
fs.ErrNotExist when accessing non-existent files or calling
os.Getwd().

For golang/go#60732

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[gopherbot]

Message from Sean Liao:

Patch Set 1: Code-Review+2

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[gopherbot]

Message from Sean Liao:

Patch Set 1:

(1 comment)

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[gopherbot]

Message from Sean Liao:

Patch Set 2: Code-Review+2

(2 comments)

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[gopherbot]

This PR is being closed because golang.org/cl/727580 has been merged.