minor fixes

* added back the HPCE logo to landing page
* activated the sticky tabs navigation feature (so navigation bar stays
  visible)
* added edit buttons to content (so users can _maybe_ help us in keeping
  our docs up to date)

docs/index.md

@@ -6,9 +6,9 @@ hide:
 
 # HPCE User Documentation
 
-![The HPCE clusters](images/merlin_cave.png){ width="650px" }
+![HPCE group](images/hpce_logo_full.png#only-light){ width="350px" }
+![HPCE group](images/hpce_logo_full_dark.png#only-dark){ width="350px" }
 /// caption
-_Within his lair, the wizard ever strives for the perfection of his art._
 ///
 
 The [HPCE

docs/merlin7/01-Quick-Start-Guide/introduction.md

@@ -1,5 +1,10 @@
 # Introduction
 
+![Merlin](../../images/merlin_cave.png){ width="400px" }
+/// caption
+_Within his lair, the wizard ever strives for the perfection of his art._
+///
+
 ## About Merlin7
 
 PSI's Merlin7 cluster is run on top of an IaaS (Infrastructure as a Service) *vCluster* on the [CSCS Alps infrastructure](https://www.cscs.ch/computers/alps). It is fully integrated with the PSI service landscape was designed to provide the same end user experience as its PSI-local predecessor clusters.