Fix typos and wording

1. fix typo in cacert path
2. fix header to indicate it's an error message
3. add log entry example
4. add sidekiq log link
5. switch "scenario" paragraphs around

doc/user/project/integrations/slack.md

@@ -28,7 +28,8 @@ Your Slack team will now start receiving GitLab event notifications as configure
 ## Troubleshooting
 
 If you're having trouble with the Slack integration not working, then start by
-searching through the sidekiq logs for errors relating to your Slack service.
+searching through the [Sidekiq logs](https://docs.gitlab.com/ee/administration/logs.html#sidekiqlog)
+for errors relating to your Slack service.
 
 ### Something went wrong on our end
 
@@ -36,7 +37,13 @@ This is a generic error shown in the GitLab UI and doesn't mean much by itself.
 You'll need to look in the logs to find an error message and keep troubleshooting
 from there.
 
-### certificate verify failed
+### `certificate verify failed`
+
+You may see an entry similar to the following in your Sidekiq log:
+
+```text
+2019-01-10_13:22:08.42572 2019-01-10T13:22:08.425Z 6877 TID-abcdefg ProjectServiceWorker JID-3bade5fb3dd47a85db6d78c5 ERROR: {:class=>"ProjectServiceWorker", :service_class=>"SlackService", :message=>"SSL_connect returned=1 errno=0 state=error: certificate verify failed"}
+```
 
 This is probably a problem either with GitLab communicating with Slack, or GitLab
 communicating with itself. The former is less likely since Slack's security certificates
@@ -58,10 +65,10 @@ puts "testing GitLab"
 Net::HTTP.get(URI('https://<GITLAB URL>'))
 ```
 
+If it's an issue with GitLab not trusting HTTPS connections to itself, then you may simply
+need to [add your certificate to GitLab's trusted certificates](https://docs.gitlab.com/omnibus/settings/ssl.html#install-custom-public-certificates).
+
 If it's an issue with GitLab not trusting connections to Slack, then the GitLab
 OpenSSL trust store probably got messed up somehow. Typically this is from overriding
 the trust store with `gitlab_rails['env'] = {"SSL_CERT_FILE" => "/path/to/file.pem"}`
-or by accidentally modifying the default CA bundle `/opt/gitlab/embedded/ssl/certs/cacertpem`.
-
+or by accidentally modifying the default CA bundle `/opt/gitlab/embedded/ssl/certs/cacert.pem`.
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-If it's an issue with GitLab not trusting HTTPS connections to itself, then you may simply
-need to [add your certificate to GitLab's trusted certificates](https://docs.gitlab.com/omnibus/settings/ssl.html#install-custom-public-certificates).
\ No newline at end of file