I dont think a template is necessary. Most letters should follow a standard format, though you just add or leave out bits that are not relevant.
As an example you could say something like
Please accept this as my notice of resignation, as stated within my contract I am giving you
You really dont need to give any other information at this stage, if you want to you can include something like “I am leaving as I am moving out of the area” (if true of course, dont ever lie in a letter!)