Manual installation - need update documentation

[Ivan Anfimov]

https://docs.openstack.org/horizon/latest/install/from-source.html

OS AlmaLinux 9.5 64 bit + tested in Debian 12 64 bit

git clone https://opendev.org/openstack/horizon -b stable/2024.2 --depth=1
cd horizon
python3 -m pip install -c https://opendev.org/openstack/requirements/raw/branch/stable/2024.2/upper-constraints.txt .

Error:

Processing /root/horizon
  Preparing metadata (setup.py) ... done
ERROR: Cannot install horizon 0.0.0 (from /root/horizon) because these package versions have conflicting dependencies.

The conflict is caused by:
    The user requested horizon 0.0.0 (from /root/horizon)
    The user requested (constraint) horizon===25.0.0

To fix this you could try to:
1. loosen the range of package versions you've specified
2. remove package versions to allow pip attempt to solve the dependency conflict

ERROR: ResolutionImpossible: for help visit https://pip.pypa.io/en/latest/user_guide/#fixing-conflicting-dependencies

[Ivan Anfimov (anfimovir)]

If we do..

curl -O https://opendev.org/openstack/requirements/raw/branch/stable/2024.2/upper-constraints.txt

remove from local file (upper-constraints.txt):
#horizon===24.0.0;python_version=='3.8'
#horizon===25.0.0;python_version>='3.9'

And run again:
python3 -m pip install -c upper-constraints.txt .

We sort this problem.