Added missing text to user documentation

docs/documentation/userguide/index.md

@@ -1,6 +1,7 @@
 # User Guide
 
-HOPR ...
+This user guide describes the installation procedure and the mesh format used in hopr and is intended for people using hopr as a
+mesh generator.
 
 ```{toctree}
 ---
@@ -20,3 +21,7 @@ the simulation code's features from a user and a developer point of view.
 
 * Chapter {ref}`userguide/installation:Installation` contains step by step instructions from obtaining the source
   code up to running hopr and visualizing the generated mesh.
+* Chapter {ref}`userguide/meshformat:HOPR HDF5 Curved Mesh Format` describes in detail how the hopr mesh format is constructed and
+  how mesh information is processed.
+* Chapter {ref}`userguide/appendix:Appendix` contains additional information, e.g., tested compiler and library versions.
+* Chapter {ref}`userguide/parameters:List of Parameters` gives an overview of all read-in parameters that are available in hopr.