new docs, up to installation procedure

docs/user-manual_usage.adoc

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+== Using the software
+WARNING: This software requires Python 3.12 or later. +
+The module *venv* and the package manager *pip* are also required.
+
+=== Downloading the source code
+IMPORTANT: Currently ({revdate}) the source code is hosted on a private Gitea instance, owned by {author}. +
+If the site is down for maintenance or temporarily unavailable please contact the webmaster via mailto:{email}[e-mail].
+
+// TO-DO: add link to direct download of package
+The source code can be acquired directly via *git*, or downloaded from the official repository on link:{repo-url}[Gitea D'Amico^].
+
+[source,bash,subs="verbatim,attributes"]
+----
+git clone {repo-url}.git {software-name}
+cd {software-name} # enter directory
+ls
+  LICENSE    docs/     output/           src/
+  README.md  glossary  requirements.txt  tests/
+----
+
+Optionally, you can access the code in the development branch by executing:
+[source,bash]
+----
+git checkout dev
+----
+
+=== Preparing the environment
+{software-name} {revnumber} requires a total of 6 modules to be installed before starting. Since installing a Python module system-wide is almost never a good idea, start by creating and activating a virtual environment.
+
+In the software folder, run:
+
+[source,bash]
+----
+# Calls venv module to create new Python virtual environment in .venv:
+python3 -m venv .venv
+# If command is successful, running ls should show a new .venv folder:
+ls -d .*
+  .venv
+# Activate venv:
+source .venv/bin/activate
+----
+
+.Most shells like Bash show very clearly when you're working inside a virtual environment.
+image::images/usage-venv.png[]
+
+At this point you're free to install the requirements through *pip*:
+
+
+
+---
+== Troubleshooting