Add 'test' to available environments in doc

[damms005]

What kind of change does this PR introduce?

• [ ] Bugfix
• [ ] Feature
• [x] Documentation
• [ ] Code style update
• [ ] Refactor
• [ ] Build-related changes
• [ ] Other, please describe:

Does this PR introduce a breaking change?

• [ ] Yes
• [x] No

The PR fulfills these requirements:

• [x] It's submitted to the dev branch (or v[X] branch)
• [ ] When resolving a specific issue, it's referenced in the PR's title (e.g. fix: #xxx[,#xxx], where "xxx" is the issue number)
• [ ] It's been tested on a Cordova (iOS, Android) app
• [ ] It's been tested on an Electron app
• [x] Any necessary documentation has been added or updated in the docs or explained in the PR's description.

If adding a new feature, the PR's description includes:

• [ ] A convincing reason for adding this feature (to avoid wasting your time, it's best to start a new feature discussion first and wait for approval before working on it)

Other information: