docs: generate table from header using a script

docs: generate table from header using a script

This adds a helper script:
$ python3 tools/list-discoverable-partitions.py <src/shared/gpt.h
<!-- generated with tools/list-discoverable-partitions.py -->
| Partition Type UUID | Name | Allowed File Systems | Explanation |
|---------------------|------|----------------------|-------------|
| _Root Partition (Alpha)_ | `6523f8ae-3eb1-4e2a-a05a-18b695ae656f` | [Root Partition] | [Root Partition more] |
| _Root Partition (ARC)_ | `d27f46ed-2919-4cb8-bd25-9531f3c16534` | ditto | ditto |
...

The output can be pasted into the markdown file. I think this works better than
trying to match the two lists by hand.