[fixdoc] webdoc: pyenv requires Tk ()

Merging branch 'fixdoc'  into 'r21'.

See merge request !1889

hugo/content/installation/py/linux.md

@@ -14,9 +14,13 @@ some point (e.g. Debian 12) disabled Pip, which terminates with
 `error: externally-managed-environment`. While this behavior can be
 overridden by a special flag, we advise against.
 
+#### Python in pyenv
+
 Rather, we recommend escaping from Python version hell by using the
 Python version manager [pyenv](https://github.com/pyenv/pyenv).
 
+Install the venerable GUI toolkit Tk (e.g. Debian package tk-dev).
+
 Prepare the shell by adding
 ```
 export PYENV_ROOT="$HOME/.pyenv"

hugo/content/installation/py/modules.md

@@ -19,6 +19,7 @@ Furthermore, a small number of fit script examples require the Python modules
   * lmfit
   * scipy
   * tqdm
+
 These are not required for _installing_ and _running_ most of BornAgain.
 However, they should be present when _building_ BornAgain
 lest some tests will fail.