Rework configuration process

Dynamically loads `config.json` on startup.

Fixes #167, #284, #449, #486

Change-Id: I9efb1079c0c88e6e0272c5fda734a367aa8f84a3

README.md

@@ -64,11 +64,6 @@ You have three options:
 - download dependencies: `yarn install`
 - start web server: `yarn start`
 
-You can fix the homeserver, so that the user can no longer define it himself.
-Either you define it at startup (e.g. `REACT_APP_SERVER=https://yourmatrixserver.example.com yarn start`)
-or by editing it in the [.env](.env) file. See also the
-[documentation](https://create-react-app.dev/docs/adding-custom-environment-variables/).
-
 #### Steps for 3)
 
 - run the Docker container from the public docker registry: `docker run -p 8080:80 awesometechnologies/synapse-admin` or use the [docker-compose.yml](docker-compose.yml): `docker-compose up -d`
@@ -76,8 +71,6 @@ or by editing it in the [.env](.env) file. See also the
   > note: if you're building on an architecture other than amd64 (for example a raspberry pi), make sure to define a maximum ram for node. otherwise the build will fail.
 
   ```yml
-  version: "3"
-
   services:
     synapse-admin:
       container_name: synapse-admin
@@ -88,7 +81,6 @@ or by editing it in the [.env](.env) file. See also the
         #   - NODE_OPTIONS="--max_old_space_size=1024"
         #   # see #266, PUBLIC_URL must be without surrounding quotation marks
         #   - PUBLIC_URL=/synapse-admin
-        #   - REACT_APP_SERVER="https://matrix.example.com"
       ports:
         - "8080:80"
       restart: unless-stopped
@@ -96,6 +88,40 @@ or by editing it in the [.env](.env) file. See also the
 
 - browse to http://localhost:8080
 
+### Restricting available homeserver
+
+You can restrict the homeserver(s), so that the user can no longer define it himself.
+
+Edit `config.json` to restrict either to a single homeserver:
+
+```json
+{
+  "restrictBaseUrl": "https://your-matrixs-erver.example.com"
+}
+```
+
+or to a list of homeservers:
+
+```json
+{
+  "restrictBaseUrl": [
+    "https://your-first-matrix-server.example.com",
+    "https://your-second-matrix-server.example.com"
+  ]
+}
+```
+
+The `config.json` can be injected into a Docker container using a bind mount.
+
+```yml
+services:
+  synapse-admin:
+    ...
+    volumes:
+      ./config.json:/app/config.json
+    ...
+```
+
 ## Screenshots
 
 ![Screenshots](./screenshots.jpg)