docs: add UI troubleshooting blurbs (#598)

website/content/docs/developing/building.mdx

@@ -28,3 +28,8 @@ If you need to cross compile boundary for another OS or architecture, use the [X
 environment variable to set this. Example: `$ XC_OSARCH=linux/amd64 make dev`
 
 For more details, please consult the [Boundary project on GitHub](https://github.com/hashicorp/boundary#build-and-start-boundary-in-dev-mode).
+
+## Troubleshooting
+
+UI assets are built inside a Docker container. If this build step fails, try
+increasing memory and swap available to Docker.