Provide a command to tell the list of files that are knowledge or instructions

### Describe the feature or problem you'd like to solve

I want to tell copilot about the application and give some instructions

### Proposed solution

Provide a command and an option to indicate which files are knowledge and instructions.
For example, I put some indication about the application in a file named `APP_DESCRIPTION.md`:

```
This application is a Node application written in Typescript and started with Vite.
It is an application made for doctors to manage theirs patients.
A doctor can... (list whatever)
A patient can... (list whatever)
...
```

Then I have another file named `TECH_SPECS.md`:

```
In this application we avoid using ORMs: we prefer RAW SQL queries.
The UI libraryis Bootstrap and stick with it, do not introduce Tailwind.
When using icons, use Font-Awesome icons
```

Then when I launch copilot, I want to do it like this:

```
copilot --background APP_DESCRIPTION.md --background TECH_SPECS.md
```

But it should be possible to do it with:

```
copilot --background "docs/*.md"
```

```

### Example prompts or workflows

_No response_

### Additional context

_No response_