First bit of documentation for Element Call added.

matrix/call/README.md

@@ -14,3 +14,46 @@ This bit is for later, but here's a nice bit of documentation to start:
 
 https://sspaeth.de/2024/11/sfu/
 
+
+# Install prerequisites
+
+Define an entry in DNS for Livekit and Call, e.g. `livekit.matrixdev.example.com`
+and `call.matrixdev.example.com`. Get certificates for them.
+
+Expand `.well-known/matrix/client` to contain the pointer to the SFU:
+
+```
+"org.matrix.msc4143.rtc_foci": [
+      {
+        "type": "livekit",
+        "livekit_service_url": "https://livekit.matrixdev.example.com"
+      }
+  ]
+```
+
+Create `.well-known/element/element.json`, which is opened by Element-web and
+ElementX to find the Element Call widget. It should contain something like
+this:
+
+```
+{
+    "call": {
+        "widget_url": "https://call.matrixdev.example.com"
+    }
+}
+```
+
+Make sure it is served as `application/json`, just like the other .well-known
+files.
+
+
+# Livekit
+
+Livekit is a small Go program that handles authorization tokens. You'll need a
+Go compiler, so install that:
+
+```
+apt install golang
+```
+
+