llms-txt: Improve inlining by retaining HTTP link to original resource

## About

The inlining process of [llms-txt](https://pypi.org/project/llms-txt/) can be improved.

## Retaining links

Currently, the inliner embeds link content, but does not retain the links. While the links per se would not be helpful for humans, it would be nice to retain references to the corresponding human-readable resource, like Junction and Turso are doing it per `Source: ` annotation right after the produced headline.

- https://docs.junction.com/llms.txt, https://docs.junction.com/llms-full.txt
- https://docs.turso.tech/llms.txt, https://docs.turso.tech/llms-full.txt

#### Source
```
- [Junction API](https://docs.junction.com/api-details/junction-api.md)
```
```
- [List Audit Logs](https://docs.turso.tech/api-reference/audit-logs/list.md): Return the audit logs for the given organization, ordered by the `created_at` field in descending order.
```
#### Result
```
# Junction API
Source: https://docs.junction.com/api-details/junction-api
```
```
# List Audit Logs
Source: https://docs.turso.tech/api-reference/audit-logs/list
```