Specify where code monitor flag is set and fix syntax (#35809)

* Specify where feature flag is set and fixed syntax

The previous version does not specify where the feature flag needed to be configured (Global Settings) and the provided syntax did not work

* Update doc/code_monitoring/how-tos/slack.md

Co-authored-by: Juliana Peña <[email protected]>

Co-authored-by: Juliana Peña <[email protected]>

Author: Christine Lovett

doc/code_monitoring/how-tos/slack.md

@@ -16,7 +16,7 @@ use that webhook's URL.
 
 ## Prerequisites
 
-- You must have the experimental feature flag `experimentalFeatures.codeMonitoringWebHooks` set to `true` in your Sourcegraph settings
+- You must have the experimental feature flag `  "experimentalFeatures": { "codeMonitoringWebHooks": true } ` set in your user, org, or global settings.
 - You must have permission to create apps inside of your organization's Slack workspace
 
 ## Creating a Slack webhook