Update README to include information on activation for restricted envs

[goanpeca]

Fixes #376

Restricted environments (no profile modifications)

If your environment does not allow modifications to ~/.profile or ~/.bashrc
(e.g. corporate self-hosted runners with restricted home directories), set
remove-profiles: "false" and source conda manually on each step:

jobs:
  restricted-env:
    name: Restricted environment
    runs-on: "ubuntu-latest"
    steps:
      - uses: actions/checkout@v5
      - uses: conda-incubator/setup-miniconda@v3
        with:
          activate-environment: myenv
          environment-file: environment.yml
          run-init: "false"
          remove-profiles: "false"
      - name: Run with conda
        shell: bash
        run: |
          source "$CONDA/etc/profile.d/conda.sh"
          conda activate myenv
          python my_script.py

[Copilot]

Pull request overview

Updates the README to document how to activate conda environments on GitHub Actions runners where shell profile files cannot be modified, addressing issue #376.

Changes:

• Added a “Restricted environments” section describing remove-profiles: "false" usage.
• Documented a manual activation approach using source $CONDA/etc/profile.d/conda.sh.
• Added an approach to auto-source activation via BASH_ENV to avoid repeating source in each step.

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[goanpeca]

@conda-incubator/setup-miniconda it seems that a proper fix for this requires adding a new input param like runCondaInit, or just runInit, true by default.

The remove-profiles input parameter could be overloaded, but they really refer to different actions. This PR adds run-init and adds a check as example and a unit test.

Thoughts on the name of the parameter or any other option you might consider better?

Thanks!