Add notice for web temrinal on GitLab.com

We have had multiple issues on why web terminals are not working on
GitLab.com, there is current work in progress to make it stable and
work in https://gitlab.com/gitlab-org/gitlab-ce/issues/52611

doc/ci/interactive_web_terminal/index.md

-# Getting started with interactive web terminals
+# Getting started with interactive web terminals **[CORE ONLY]**
 
 > [Introduced](https://gitlab.com/gitlab-org/gitlab-ce/issues/50144) in GitLab 11.3.
 
@@ -6,10 +6,9 @@ Interactive web terminals give the user access to a terminal in GitLab for
 running one-off commands for their CI pipeline.
 
 NOTE: **Note:**
-This is not available for the shared Runners on GitLab.com.
-To make use of this feature, you need to provide your
-[own Runner](https://docs.gitlab.com/runner/install/) and properly
-[configure it](#configuration).
+GitLab.com does not support interactive web terminal at the moment. Please
+follow [this issue](https://gitlab.com/gitlab-org/gitlab-ce/issues/52611) for
+progress. 
 
 ## Configuration