Recommend modifying mp4edit to use system path instead of current directory #12

Hello,

In setting this program up (great work by the way!) I found that it was easier to modify the script on lines 180, 201, and 261 to call $`mp4edit instead of $`./mp4edit. This allows the user to add mp4edit to path so they do not need to relocate it from an existing install to the working directory.

Thanks!