Update hero text

[kristenwomack]

Updates to the hero text To give folks a bit more context on what to expect from the templates.

Above the search bar

• Current: A community-contributed template gallery built to work with the Azure Developer CLI.
• New text: An open-source template gallery maintained by Microsoft. Select an application and deploy to Azure using the Azure Developer CLI (azd). Each template is a fully working application with infrastructure as code for you to get started.

Below the search bar

• Current: Not familiar with the Azure Developer CLI (azd)?Learn more
• Updated: New to the Azure Developer CLI (azd)? Welcome! Learn more in our docs.

cc: @spboyer @gkulin