Added cross-assembly links section

docs/maps.en.md

@@ -20,6 +20,7 @@ This tutorial is "work in progess", hence its worth checking it from time to tim
 * 2020-12-17: Audio: removed external URLs. **IMPORTANT:** If you want to include streams please contact us!
 * 2020-12-20: Starter kit added.
 * 2020-12-22: World-Exit added.
+* 2020-12-22: Cross-Assembly Links added.
 
 ## Known Bugs
 Following bugs are known and worked on:
@@ -201,6 +202,15 @@ A example map might look like this:
 ### Entrypoint / Lobby / Exit
 We create central Entrymaps to join the world and lead to the different assembly maps. Please drop us an email via [world@rc3.world](mailto:world@rc3.world) naming your assemblyname, that we can reserve an exitpoint to your assembly. Besides that we would ask you to reserve a spot for an exit back to the lobby maps on your map. Tiles and the address for the jump will be provided by us via mail.
 
+### Crossy-Assembly links
+There will be placeholders which get automatically replaced by the right url. Example for a placeholder: `{<SLUG>/map.json#YourStartLayer}`. **< and > are important and need to stay in the placeholder!**
+
+You can find _your slug_ in the Maschinenraum under Organisational Data -> Basic Data -> "Slug".
+
+If you want to link to the foobar assembly for example and the foobar assemblys slug is `foobar`, the value for the exit layer would be `{<foobar>/main.json}`.
+
+Attention: This does **not** work for the test instance.
+
 ### Testing
 For testing you may put the map on any server reachable by https and embed the URL in our test instance. Lets assume your map is stored under _https://example.com/mymaps/foo.json_ then the URL to test it would be *https://test.visit.at.wa-test.rc3.cccv.de/_/global/example.com/mymaps/foo.json*. The option to load external maps is just for testing and will be disabled for rC3.
 
@@ -209,5 +219,9 @@ You might need to set the matching CORS Headers on the server serving the map.
 ## Hosting your own Instance
 Please do not try to host your own instance! We will not allow jumps to external instances!
 
+## Big Blue Button
+We like BBB, but the rC3.world already contains a stable inclusion of jitsi, which we host on dedicated hardware. We currently do not have the resources to make BBB embedding possible.
+Please don't expect BBB for the rC3.world and use jitsi instead.
+
 ## Infrastructure
 The infrastructure is kindly sponsored by <a href="https://www.hetzner.com/de/cloud"><img src="img/hetzner-logo.svg" alt="hetzner online" width="100px" /></a>.