Add changelog entries for GitLab v15.5 and v15.6

Closes #76 (closed)

docs/software/gitlab/changelog.md

@@ -2,6 +2,28 @@
 title: Changelog
 ---
 
+## 2022-12-12 - GitLab 15.6
+
+* Update GitLab to version 15.6
+    * [CI/CD variable support in rules:exists configuration][15-6-exists-in-rules]
+    * [Support for special characters in CI/CD variables][15-6-special-characters]
+    * All details are available in the [Release Post][15-6-release-post]
+
+[15-6-exists-in-rules]: https://about.gitlab.com/releases/2022/11/22/gitlab-15-6-released/#cicd-variable-support-in-rulesexists-configuration
+[15-6-special-characters]: https://about.gitlab.com/releases/2022/11/22/gitlab-15-6-released/#support-for-special-characters-in-cicd-variables
+[15-6-release-post]: https://about.gitlab.com/releases/2022/11/22/gitlab-15-6-released/
+
+## 2022-11-21 - GitLab 15.5
+
+* Update GitLab to version 15.5
+    * [Autocomplete suggestions in the Content Editor][15-5-auto-completion]
+    * [Email notification when two-factor OTP attempt is wrong][15-5-2fa-email]
+    * All details are available in the [Release Post][15-5-release-post]
+
+[15-5-auto-completion]: https://about.gitlab.com/releases/2022/10/22/gitlab-15-5-released/#autocomplete-suggestions-in-the-content-editor
+[15-5-2fa-email]: https://about.gitlab.com/releases/2022/10/22/gitlab-15-5-released/#email-notification-when-two-factor-otp-attempt-is-wrong
+[15-5-release-post]: https://about.gitlab.com/releases/2022/10/22/gitlab-15-5-released/
+
 ## 2022-10-06 - GitLab 15.4
 
 * Update GitLab to version 15.4