doc: build local package

[JosiahParry]

The vignette https://r-wasm.github.io/rwasm/articles/rwasm.html shows how to use build() to build an existing CRAN package or you can use a remote url. However, using build(".") to install a package as one would do with pak does not work.

It would be great if it could be documented how to build a package locally.

[JosiahParry]

For further context / reproducibility, this is the workflow I've got going so far:

• clone b64 and cd into it
• mkdir output
• docker pull ghcr.io/r-wasm/webr:main
• docker run -it --rm -v ${PWD}/output:/output -w /output ghcr.io/r-wasm/webr:main R

install.packages("pak")
pak::pak("r-wasm/rwasm")

Now from here is where we would build the package. But each various invocation of build() i can come up with ends up with this error:

build("b64=local::.")
Error in if (startsWith(url, "file:")) "internal" else "libcurl" :
  missing value where TRUE/FALSE needed

[JosiahParry]

Got it. So the approach here is to use a "normal" R session and build the tar.gz either with devtools::build() or R CMD build then inside of webR using rwasm::build("./path/to/pkg_ver.tar.gz")