Angle Bracket are the easiest and the fastest method available to install your shelves.
Really! It only takes about 5 to 10 minutes to install your shelves once you have all of your tools and materials available.
Hammer - Pencil - Tape Measure - Ladder
There should be at least 8" distance between the top of your trim and the ceiling so that you will have enough room to use the hammer to drive in the nails supporting the Angle Bracket.
Your window must have a "depth" of at least 2" for the shelves to hang properly.