Setting up a landing page at https://spdx.github.io to prevent 404

[bact]

• Currently the spec is available on https://spdx.github.io/spdx-spec/

• https://spdx.github.io alone brings 404 file not found

• Propose to setup a page at https://spdx.github.io that either

  1. immediately redirects to https://spdx.github.io/spdx-spec/ or https://spdx.dev OR
  2. contains a minimal "landing page" content with a link to https://spdx.github.io/spdx-spec/ (and may be other active development projects)

• This requires a new repo under the name spdx.github.io (https://github.com/spdx/spdx.github.io). See details here: https://docs.github.com/en/pages/quickstart

[bact]

See also

• 404 page isn't working #378

[goneall]

Moving this to 3.1 milestone