According to my sources 饣 means "food" or "eat". Since when do people eat jewelry?
According to zdic.net, 饰 is formed of 巾, 人, and 食 (饣). 食 (饣) is the sound component, while the other portion suggests the meaning.
The dictionary explains the character's components this way: 形声。从巾,从人,食声。人佩巾有装饰作用。 So, it's a 'pictophonetic' character which signifies a person wearing or adorned with a cloth, thus having the effect of decoration.
If you're interested in this kind of composition theory, you can look up more on the various ways characters were composed. 形声 being one of the ways.
Zdic.net is great for this kind of thing. When you look up a character or word you can click 详细解释 for more in-depth info. Yellowbridge is also decent for this kind of question.