[DOCS] Broken links on Home page to installation and user guide sections

[iuliaferoli]

When something is wrong with the documentation:

• please tell us clearly where the mistake is
• explain why the mistake is confusing or wrong
• suggest a better tone/alternative

It is also perfectly fine to discuss the examples in the documentation here as well.

These are the broken references from the Installation and Usage sections:

For more installation options and details, check the installation section.
The link https://koaning.github.io/installation doesn't exist --> should be https://koaning.github.io/scikit-lego/installation/

To see more examples, please refer to the user guide section.
The link https://koaning.github.io/user-guide/datasets doesn't exist --> should be https://koaning.github.io/scikit-lego/user-guide/datasets/