Add some more content in architecture

Signed-off-by: Karel van Klink <karel.vanklink@geant.org>

docs/architecture/index.md

@@ -50,7 +50,7 @@ On top of this 'base layer' services can be deployed. Some examples of offered s
 
 ## Principles
 
-For reference:
+### For reference
 
 * All network operations are automated, requiring no operator steps beyond the instantiation of intent.
 * Changes applied to individual network element are fully declarative, vendor-neutral, and derived from the network
@@ -58,3 +58,9 @@ infrastructure from the high-level, network-wide intent.
 * Any network changes are automatically halted and rolled back if the network displays unintended behaviour.
 * The infrastructure doesn't allow operations that violate network policies. 
 [Source.](https://static.googleusercontent.com/media/research.google.com/en//pubs/archive/45687.pdf)
+
+### Other principles
+
+* Automatic check evaluate all changes
+* After passing pipelines, all changes are merged into the `main` branch. These pipelines run once a change is 
+peer-reviewed and approved.