Documentation outdated

# Description
I tried to start using PyWPS. I had some problems I want to hint at at the documentation at the [website documentation](https://pywps.readthedocs.io/en/latest/install.html). Background: For a study project I shall get a cost path algorithm running with pywps.

First of all, the documentation refers to PyWPS 4.3, while the version in pypi is 4.5.2. Additionally, it is asked to install `python-gdal` on Ubuntu. When I checked correctly it exists for Ubuntu 18.04 only. I could not install pywps with the pip command `$ sudo pip install -e git+https://github.com/geopython/pywps.git@master#egg=pywps-dev`. But I could install the version from pypi, which is not listed in the documentation.
Then I wanted to test my installation with `pywps-flask`. Flask is not listed in the requirements of pywps perhaps that is a good idea. When I you refer to `pywps-flask` on several sites.

Travis-ci linked is: `https://travis-ci.org/github/geopython/pywps`. Which is not the current version. The last build attempt was about a year old.

I could not get pywps-flask running. I used the method mentioned on [pypi](https://pypi.org/project/pywps/). I to install pywps-flask I needed the `https link` instead of the `git link`. Even after turning of the firewall. Then I tried to run it, but it looks to me, that the versions of pywps and pywps-flask do not match?
The stacktrace shows that: `pywps-flask\processes\area.py` tries to import `temp_dir` from `pywps.pywpsserver`. But my installation of pywps 4.5.2 does not find any modul pywpsserver.
While am I at it:
pycharm shows a warning for `pywps-flask/demp.py` because `pywps.configuration` is not added in the __init__.py.
`pyflask\process\feature_count.py` try to import `from pywps.app.basic import xpath_ns`. With `xpath_ns` is not existing. `pywps-flask\processes\grass_buffer.py` uses grasses. Which should be hinted how to get it?

# Environment

- operating system: Ubuntu 20.04
- Python version: 3.10
- PyWPS version: 4.5
- source/distribution: PyPI