freebsd-tips: Use a fetchable URL as example

MFC after: 3 days

(cherry picked from commit ffe6afc4f0121f1909f2fa88694228f771dd3fcb)

freebsd-tips: Fix the description of fetch(1) to match the command

Reported by: jrtc27
MFC with: ffe6afc4f0121f1909f2fa88694228f771dd3fcb

(cherry picked from commit 167897510919a76740eca0d79713abbd088660fe)