Update feature flag target users documentation

Target users are defined per environment now

doc/user/project/operations/feature_flags.md

@@ -75,7 +75,7 @@ To define specs for each environment:
 1. Set the status and rollout strategy of the additional spec. This status and rollout strategy combination takes precedence over the default spec since we always use the most specific match available.
 1. Click **Create feature flag** or **Update feature flag**.
 
-![Feature flag specs list](img/specs_list.png)
+![Feature flag specs list](img/specs_list_v12_6.png)
 
 NOTE: **NOTE**
 We'd highly recommend you to use the [Environment](../../../ci/environments.md)
@@ -119,17 +119,15 @@ CAUTION: **Caution:**
 If this strategy is selected, then the Unleash client **must** be given a user
 ID for the feature to be enabled. See the [Ruby example](#ruby-application-example) below.
 
-### Target users strategy
+#### User IDs
 
-> [Introduced](https://gitlab.com/gitlab-org/gitlab/issues/8240) in GitLab 12.2.
+> [Introduced](https://gitlab.com/gitlab-org/gitlab/issues/8240) in GitLab 12.2. [Updated](https://gitlab.com/gitlab-org/gitlab/issues/34363) to be defined per environment in GitLab 12.6.
 
 A feature flag may be enabled for a list of target users. It is implemented
 using the Unleash [`userWithId`](https://unleash.github.io/docs/activation_strategy#userwithid)
 activation strategy.
 
-The feature will always be enabled for all users in the list across all environments even if the matching environment spec **Status** is disabled.
-
-![Feature flag target users](img/target_users_v12_2.png)
+User IDs should be a comma separated list of values. For example, `user@example.com, user2@example.com`, or `username1,username2,username3`, etc.
 
 CAUTION: **Caution:**
 The Unleash client **must** be given a user ID for the feature to be enabled for