Add why matrix

chat/matrix/why.markdown

+# Why matrix as a chat system?
+
+Institutions of higher education (e.g. universities) with a Matrix service:
+
+<img src="/media/chat/federation_map.svg" alt="Matrix federation map of institutions of higher education">
+
+There are many services and programs for instant electronic communication. Matrix was chosen because it has the following characteristics:
+
+- Open standard (no technical dead end)
+- Communication protocol for federated real-time communication (no isolated solution but like e-mail with worldwide connectivity)
+- Differentiated communication possible (1:1, multiple teams, topic-specific)
+- Decentralized, persistent and interoperable communication (no central control instances, connectable with other protocols and tools)
+- Data protection: end-to-end encryption standard in 1:1 conversations and (group) rooms, can be switched off in the latter
+- Web application + desktop client + mobile apps available
+  - The contacts on your own cell phone are not automatically passed on to third parties (no address book upload)
+- Existing successful security audit
+- Autonomy and control: locally installable (server location ETH Hönggerberg)
+- Recognize the presence status
+- Active further development
+- Up-and-coming use by other scientific institutions (e.g. lots of German universities)
+
+Further informationen: https://matrix.org/docs/chat_basics/
+
+Detailed explanation of technical terms: https://matrix.org/docs/older/faq/#definitions
+