Federal should be lowercase

See https://digital.gov/style-guide/#grammar-and-spelling-2.

app/routes/docs.contributing._index.mdx

@@ -37,7 +37,7 @@ Here are some more specific ways that _you_ can help.
 - **Improve design and accessibility.**
   We are constantly seeking to improve the GCN user experience. Look for issues in GitHub that are marked <GitHubLabel owner="nasa-gcn" repo="gcn.nasa.gov" name="frontend"/>.
 
-  We use the [US Web Design System](https://designsystem.digital.gov), an open source design language and front end framework that is common to many Federal agencies. US Web Design System components for [React](https://reactjs.org) are provided by [react-uswds](https://github.com/trussworks/react-uswds).
+  We use the [US Web Design System](https://designsystem.digital.gov), an open source design language and front end framework that is common to many U.S. federal agencies. US Web Design System components for [React](https://reactjs.org) are provided by [react-uswds](https://github.com/trussworks/react-uswds).
 
 - **Add new features to the web site.**
   We have lots of ideas for new features, visualizations, and ways to interact with GCN data. We bet you have lots of ideas too! Look for issues in GitHub that are marked <GitHubLabel owner="nasa-gcn" repo="gcn.nasa.gov" name="frontend"/> or <GitHubLabel owner="nasa-gcn" repo="gcn.nasa.gov" name="backend"/>.