Update nginx configuration to allow for larger uploads.

DEPLOY.md

@@ -214,6 +214,9 @@ server {
     server_name your.server.name; # EDIT THIS
     merge_slashes off;
 
+    # Nginx default to only allow 1MB uploads. 
+    client_max_body_size 20M;
+
     location /_matrix/ {
         proxy_pass http://127.0.0.1:6167$request_uri;
         proxy_set_header Host $http_host;