[BUG]: Logo images in README are not suited for dark theme

### Expected Behavior

The included logos should be readable with both dark and light themes.

### Actual Behavior

When using the dark theme, the contrast on the logos is not suffcient.

### Terraform Version

terraform --version
Terraform v1.14.3
on darwin_arm64
+ provider registry.terraform.io/hashicorp/archive v2.7.1
+ provider registry.terraform.io/hashicorp/aws v6.34.0
+ provider registry.terraform.io/hashicorp/null v3.2.4
+ provider registry.terraform.io/hashicorp/random v3.8.1
+ provider registry.terraform.io/hashicorp/tls v4.2.1

### Affected Resource(s)

N/A

### Terraform Configuration Files

```hcl
N/A
```

### Steps to Reproduce

Open https://github.com/integrations/terraform-provider-github, set github theme to Dark (see https://docs.github.com/en/get-started/accessibility/managing-your-theme-settings )

### Debug Output

```shell

```

### Panic Output

```shell

```

### Code of Conduct

- [x] I agree to follow this project's Code of Conduct