Tidy up the bits of the instructions

Three unrelated small changes:

Updates to the final pages of the instructions.

• From #402 (closed), add a link to the handbook for first set-up

closes: #402 (closed)

Update to the way the C270 camera preparation is presented

• From #388 (closed) Stop using "*Some text" as a way to draw attention to the need to disassemble the C270 in the RMS section of the alternative optics page.

Making an info box is the same level of highlight as for the tall stand for the infinity optics, which seems appropriate. I tried other methods, including [i] tags with a link, but they all looked ugly.

closes: #388 (closed)

Update the Arduino workaround instructions for the sangaboard sketch

• From #295 (closed), make sure there is no reference to the bootloader.

closes: #295 (closed)