Improve installation docs

[PabloCarmona]

Description and motivation

The current installation docs are not clear and have missing info:

• [ ] OpenBLAS bindings not working.\
• [ ] Dependecies for aihwkit not installed along with the pip package. Need to be installed separately.
• [ ] Conda forge builds only works for linux-64 systems. Need to let the user know this until we create builds for osx-arm64/osx-amd64.

Proposed solution

Create a new docs for installation and reorganize some parts of it. Add the needed info to guide the user better.