[i682b] hugo build/install: update on Debian ()

Merging branch 'i682b'  into 'r21'.

See merge request !1816

hugo/content/installation/building/unix/third-party.md

@@ -56,13 +56,18 @@ very similar.
 Install required packages:
 ```
 $ sudo apt-get install build-essential git cmake \
-  libgsl-dev libfftw3-dev libcerf-dev libtiff5-dev \
+  libgsl-dev libfftw3-dev libtiff5-dev \
   python3 python3-dev python3-pip python3-numpy python3-matplotlib python3-lmfit \
   libboost-dev libboost-iostreams-dev \
   libboost-program-options-dev libboost-regex-dev \
   libcerf-dev qt6-base-dev qt6-svg-dev
 ```
 
+Note: Normally we should also depend on `libcerf-dev`,
+which however is presently outdated.
+Therefore Debian users should install libcerf from source,
+https://jugit.fz-juelich.de/mlz/libcerf.
+
 ### OpenSuse
 Install required packages:
 ```

hugo/content/installation/install/linux.md

@@ -27,7 +27,8 @@ $ python -m pip install bornagain
 A BornAgain Debian/Ubuntu package (Python and GUI) is provided by external maintainers
   at https://tracker.debian.org/pkg/bornagain.
 
-The only drawback is that versions may be lagging behind by a couple of months.
+The only drawback is that versions may be lagging behind,
+in *unstable* by a couple of months, in *stable* by several years.
 
 #### Install using our installer