docs(config): notice users about optional but used plugin

[sensorario]

Reading that a plugin is optional can make confusion: readers may not install plugin.
Users can not undersand next steps of documentation, based on this plugin.

[GitCop]

There were the following issues with your Pull Request

• Commit: e8c1ad8
  • Your commit message body contains a line that is longer than 80 characters
  • Commits must be in the following format: %{type}(%{scope}): %{description}

Guidelines are available at http://karma-runner.github.io/0.13/dev/git-commit-msg.html

---

This message was auto-generated by https://gitcop.com

[googlebot]

Thanks for your pull request. It looks like this may be your first contribution to a Google open source project, in which case you'll need to sign a Contributor License Agreement (CLA).

📝 Please visit https://cla.developers.google.com/ to sign.

Once you've signed, please reply here (e.g. I signed it!) and we'll verify. Thanks.

---

• If you've already signed a CLA, it's possible we don't have your GitHub username or you're using a different email address. Check your existing CLA data and verify that your email is set on your git commits.
• If you signed the CLA as a corporation, please let us know the company's name.

[GitCop]

There were the following issues with your Pull Request

• Commit: db6f7f9
  • Invalid type. Valid types are feat, fix, docs, style, refactor, test, chore, revert

Guidelines are available at http://karma-runner.github.io/0.13/dev/git-commit-msg.html

---

This message was auto-generated by https://gitcop.com

[dignifiedquire]

Probably better: The following Jenkins plugin, but the next guidelines are based on it:

[dignifiedquire]

Thanks, there is a space too much in your commit message before the (

[GitCop]

There were the following issues with your Pull Request

• Commit: c5463c1
  • Commits must be in the following format: %{type}(%{scope}): %{description}

Guidelines are available at http://karma-runner.github.io/0.13/dev/git-commit-msg.html

---

This message was auto-generated by https://gitcop.com

[sensorario]

Mmmm. Gitcop is amazing but, ... can you help me to fix this one: "https://ci.appveyor.com/project/zzo/karma/build/1.0.175"

I followed guidelines. Or not?

[dignifiedquire]

I think you missed the is optional

[dignifiedquire]

@sensorario appveyor isn't properly setup so you can ignore that. The commit message is fine now :)

[dignifiedquire]

Thanks