Change: Update README regarding installation and updates (#448)

For Python devs familiar with poetry these steps are mostly obvious. But
this is not the case for new or outside contributors.

---------

Co-authored-by: Joseph <[email protected]>

README.md

@@ -9,26 +9,41 @@ https://greenbone.github.io/docs/
 
 For a manual build locally Python >= 3.9 and [poetry] is required.
 
-## Install Dependencies
+## Install Poetry
+
+To install poetry it is recommended to use [pipx]. pipx can be installed with
+the following command on Debian based systems:
+
+```sh
+sudo apt install pipx
+```
+
+Install poetry using pipx
 
-To install poetry it is recommended to use [pipx]
 ```sh
 python3 -m pipx install poetry
 ```
 
-To install the project dependencies via [poetry] run
+## Install and Upgrade Dependencies
+
+When building the docs you should ensure that all the dependencies are installed
+and up to date. To install for the first time or to update the project
+dependencies via [poetry] run:
+
 ```sh
-poetry install
+poetry install --no-root
 ```
 
+You should run this command once a week to install the latest dependencies.
+
 ## Manual Build
 
-After installing [poetry] and the project's dependencies, the docs can be build with
+After installing [poetry] and the project's dependencies, the docs can be built with:
 ```sh
 poetry run make html
 ```
 
-To open the generated HTML docs with Firefox you can run
+To open the generated HTML docs with Firefox you can run:
 
 ```sh
 firefox _build/html/index.html
@@ -37,17 +52,35 @@ firefox _build/html/index.html
 ## Auto Rebuild
 
 Alternatively it is possible to start a local HTTP server that automatically
-rebuilds the docs on every file change
+rebuilds the docs on every file change:
 
 ```sh
 poetry run make livehtml
 ```
 
-To open the served docs with Firefox you can run
+To open the served docs with Firefox you can run:
 
 ```sh
 firefox http://127.0.0.1:8000
 ```
 
+## Starting From Scratch
+
+If something is wrong with your dependencies or you just want to re-start from
+a clean environment you need to remove the [virtual environment](https://docs.python.org/3/library/venv.html).
+First of all ensure that poetry's virtual environment is placed within the
+project:
+
+```sh
+poetry config virtualenvs.in-project true
+```
+
+Afterwards the virtual environment including all installed dependencies can be
+deleted:
+
+```sh
+rm -rf .venv
+```
+
 [poetry]: https://python-poetry.org/
 [pipx]: https://pipx.pypa.io/stable/