This Pull Request closes#1948.
It changes the following:
- set `readme` in `boa_engine` so `README.md` will be published to crates.io
- remove unnecessary `exclude` field from `Cargo.toml` in all apps
I was unsure whether using a path outside of the workspace root was allowed for `readme` since it [doesn't get included in the release tarball](https://github.com/rust-lang/cargo/issues/5911), but this exact path is used by [juniper](https://github.com/graphql-rust/juniper/blob/master/juniper/Cargo.toml#L13) and [seems to work there](https://crates.io/crates/juniper). I believe `cargo publish` does a bit more than just uploading the tarball, including pulling the `readme` from any arbitrary path.
The default behaviour of `cargo package`/`cargo publish` if neither `exclude` or `include` is specified is to include all files from the package root, excluding
- dotfiles
- .gitignore'd files
- subpackages (any subdirectory with a `Cargo.toml` file)
- the `/target` directory
There's no need to explicitly exclude files from the parent directory since they're already excluded by default. This can be verified by running `cargo package --list` inside any workspace app:
```plain
$ cd boa_wasm
$ cargo package --list
.gitignore
Cargo.toml
Cargo.toml.orig
src/lib.rs
```
You can read more [here](https://doc.rust-lang.org/cargo/reference/manifest.html#the-exclude-and-include-fields).