Improve presentation of available package parsers docs

In https://scancode-toolkit.readthedocs.io/en/stable/reference/available_package_parsers.html the table is too wide and forces to scroll.
I think we need a different presentation entirely.
One idea:
- a top level table with one row each supported package type:
- package type, type description, link to a secondary section below
- then for each type, a list of repeated small tables, one for each parser/file type:

| Package type | pypi |
|-------------------|-------------|
| Description | lorem ipsum |
| Path Patterns | lorem ipsum |
| Package type | lorem ipsum |
| Datasource ID | lorem ipsum |
| Primary Language | lorem ipsum |
| Documentation URL | lorem ipsum |