docs: README in @carbon/pictograms-react has incorrect usage information

[metonym]

What package(s) are you using?

• carbon-components
• carbon-components-react

Detailed description

The README for carbon/packages/pictograms-react contains incorrect usage information.

The usage section reads:

import { Add24 } from '@carbon/pictograms-react';

However, there is no Add24 export from pictograms.

Additionally, the Usage footnote links to the icon library in the Carbon Design System docs.

Note: if you would like to find the import path for an icon, you can reference our Icon Library

Proposed changes

1. Use a valid example in the Usage section
2. Link to the pictograms documentation in Carbon

- import { Add24 } from '@carbon/pictograms-react';
+ import { Airplane } from '@carbon/pictograms-react';

- Note: if you would like to find the import path for an icon, you can reference our [Icon Library](https://www.carbondesignsystem.com/guidelines/icons/library/)
+ Note: if you would like to find the import path for a pictogram, you can reference our [Pictogram Library](https://www.carbondesignsystem.com/guidelines/pictograms/library)

Additional information

Once the README is updated, the package should be patched so that the changes are propagated to the npm/yarn registries.