Updated Changelog (markdown)

Changelog.md

@@ -6,6 +6,25 @@ This change log tracks the releases on our [pilot server](https://recodex.mff.cu
 | 17.2.2022     |  v2.2.1  |  v2.2.1  |  v1.7.4  |  v1.3.0  |  v1.0.0  |  v1.1.0  |
 | 11.2.2022     |  v2.2.0  |  v2.2.0  |  v1.7.4  |  v1.3.0  |  v1.0.0  |  v1.1.0  |
 
+## 20.9.2022
+
+- User may set up an iCal export link (resolving issue #393)
+- Reimplementing source code viewers
+- Adding a new page with all solution source codes together
+- Implementing diff feature to compare two solution source files
+- Users may select in UI config whether to display First name or Last name first in user listings and the actual format of date time fields
+- Teachers may invite new students to ReCodEx (registration by invitation)
+- Group admins may create invitation links (that can be sent via alternate channels or published outside ReCodEx) for registered users so they can join groups
+- Splitting group detail page into assignments page and students page
+- Fixing issue #459
+- Upgrading package dependencies
+- Various UX and appearance improvements
+- Full migration to PHP 8.1 (older versions no longer supported)
+- Updating package dependencies
+
+> Db migration needed, gcc, g++, fpc, flex and flex+bison compilation pipelines need to be updated from the [runtimes repository](https://github.com/ReCodEx/runtimes)
+
+
 ## 14.3.2022
 - Switching API strictly to PHP 7.4 (PHP 7.3 support dropped!)
 - Support for compile arguments for C and C++ environments added