When a board is manufactured, the board house will use a milling tool to cut the final shape of the board out of the larger PCB panel. If you have 90 degree (or more acute) angles on the corners of your board they can end up pretty sharp.
For prototypes it is common to just file the sharp edges off, however with just a bit more effort we can round the sharp corners of the board in Eagle so the milling operation will take care it for us. While there are more than one way to skin this particular cat, the Miter tool makes it extremely easy.
Select the Miter tool and choose your desired radius (in mils due to the grid settings). Then simply click on each of the corners you want to round.
Next we'll add some text to the tPlace (21) and bPlace (22) layers to be printed on the board to help us identify which pins are which. These sets of text or graphics are referred to as "silk screens" or "silks" because of the silk screen printing processed used. The the same process is often used to print t-shirts!
Before we add our text, let's check the handy manufacturing extension to see what the board will look like. To make sure it's enabled open the Options>User interface... menu and make sure the manufacturing checkbox is checked in the Extensions section
Next click on the Manufacturing extension to load the board preview. Looking at the preview of the board that it provides, we can see that we forgot to remove the labels for the headers.
Use the delete tool to remove the header labels if the are still there then make sure the tPlace (21) layer is selected. Click on the Text tool and you will be prompted to enter the text that you want to add to the board. Start with the VCC and click OK. The text tool acts like a stamp, placing the selected text wherever you click.
With the text tool set to your chosen text you can adjust the size and ratio selectors to adjust the size and thickness of the text. Once you are happy with a size, click next to the VCC pin of the INA219 header to add it to the silk screen. Once the first label is place, right click to rotate the tool and apply another label next to the Trinket header's VCC pin.
Repeat this process to add as many or as few labels as you wish. I highly suggest that you have at minimum at least one pin of each header labeled so that you know how to orient the Trinket an INA219 breakout.
As a last step we should double check the board before sending it off to have it manufactured. First use the manufacturing extension to verify that the board and silks look how you would like them to. Lastly run another design rule check to verify there aren't any lingering issues
In my case there was a wire stub error which is an extra unused piece of a trace. You can address wire stubs by simply using the ripup tool to remove them. Address any DRC errors that show up, then save and we're ready to send the board out to be manufactured!