Updates the README to resolve #10

[signus]

Based on #10 the issue is itself not actually with the install but the instructions provided to install the ASDF plugin for R.

This is just a single line change in the README to resolve the message R is invalid. Name may only contain lowercase letters, numbers, '_', and '-':

asdf plugin-add r https://github.com/asdf-community/asdf-r.git

[signus]

Note that the hygiene check seems to be based on an outdated workflow that does not match with the current Makefile:

asdf-community/.github/.github/required-workflows/hygiene.yml

name: Hygiene

on:
  - pull_request

jobs:
  hygiene:
    name: Hygiene

    runs-on: ubuntu-latest

    steps:
      - name: Checkout code
        uses: actions/checkout@v3

      - name: Set-up Homebrew
        uses: Homebrew/actions/setup-homebrew@master

      # Dependencies
      - run: brew install shellcheck shfmt

      # Check formatting with shfmt
      - run: make format-check

      # Check linting with shellcheck
      - run: make lint

[flying-sheep]

You need to also fix the example lines here:

asdf-r/README.md

Lines 40 to 44 in f1e4b8b

	```R_EXTRA_CONFIGURE_OPTIONS=--enable-R-shlib asdf install R <version>```
	maibe you'll need Cairo as well:
	```R_EXTRA_CONFIGURE_OPTIONS='--enable-R-shlib --with-cairo' asdf install R <version>```

Should be asdf install r, not R