The different features are varied in nature, so there isn't any easy way of summarizing them. Use the cpufeature.h file to identify them, then look them up (even just in wikipedia), it will give you an idea what each one means.
It isn't as simple as just a list of instructions. Some of the features are changes to the way in which the processor works rather than additional instructions (for example, the page size features).
I don't think you will find a comprehensive document that describes them all (apart from the Intel and AMD manuals, such as
the ones here, which may give more detail than you require.
