Add docs for tester groups (#2747)

* Initial docs for tester groups

* restructuring and editing

* Edit section header

* Restructure

* Improve wording

* Fix typo

content/yaml-publishing/tester-groups.md

@@ -0,0 +1,53 @@
+---
+title: Build distribution to tester groups
+description: Distribute app builds to groups of testers
+weight: 3
+aliases:
+---
+
+Tester groups are a convenient way to manage testers for your app in the Codemagic UI and distribute app builds to a group of email addresses outside of Codemagic. Testers who have confirmed their email addresses will receive an email with the app artifacts after every successful build of the workflow.
+
+{{<notebox>}}
+Note that tester groups are only available for **teams** and apps using the `codemagic.yaml` configuration.
+{{</notebox>}}
+
+## How to distribute builds to tester groups
+
+Two steps are required to automate build distribution to tester groups.
+
+### Step 1. Create a tester group
+
+On the **Tester groups** tab in your app settings, create a new tester group and invite testers by entering their email addresses. You can invite many testers at once, provided that email addresses are separated by a comma or a new line.   
+
+Note the name of the tester group as you will have to use it in the `codemagic.yaml` file.
+
+### Step 2. Update the codemagic.yaml file
+
+In order to send testers publishing emails with app artifacts, the names of the tester groups must be specified in the `publishing` section of `codemagic.yaml` as follows:
+
+{{< highlight yaml "style=paraiso-dark">}}
+publishing:
+  tester_groups:
+    - tester_group_1
+    - tester_group_2
+{{< /highlight >}}
+
+This allows you to configure which workflows publish to tester groups and have different workflows publish to different groups. 
+
+Tester groups receive an email only when the workflow builds successfully. If the build fails, tester groups are not notified. 
+
+## Testers management
+
+Each invited tester will receive an email to confirm their consent to receive build emails with app artifacts. Only confirmed testers will receieve emails with app artifacts. 
+
+In the UI, testers will have one of the following statuses:
+
+* **"Active"** -- tester is eligible to receieve emails on successful app builds.
+* **"Pending"** -- tester has not confirmed the invitation and will not receive any further emails until they confirm.
+* **"Rejected"** -- delivery to that email has failed (e.g. email bounced) and the tester will not receive any further emails.
+
+You can add new testers and remove existing ones anytime.
+
+## Limit on the number of testers
+
+By default, the number of testers is limited to 20 across all applications in the team. Please get in touch with us should you require a higher limit.