If you want to add a consistent sales invoice note to all of your invoices, navigate to the "Your Crunch" tab and select the "Dashboard":
Then in the middle of the page, you'll see the "Account Settings" area. Click on "Document Settings":
You can then type the text you wish to appear on your note in the box. Please note that you should avoid pasting text in to the text editor box as this can cause problems when producing the invoice pdf.
Clicking on "Save settings" will then take you back to the "Your Crunch" dashboard with a confirmation message that your note has been saved.
Note: A default sales invoice note will be overwritten by either the note typed when drafting an invoice and / or overwritten by the default invoice note for the specific client you are invoicing.