docs(readme): enhance leap-to-line example code

[rish987]

Piggybacking off of my last PR, I also wanted to propose some enhanced code for using Leap to leap to a particular line, which effects the following:

• places the targets at the first non-whitespace character on a line (since that is most likely where you are going to be looking when you leap to a line)
• parameterized to also let you put the targets at the end of each line
• parameterized to also let you jump to empty lines

[ggandor]

Hi, thanks! Feel free to share this in a gist (or plugin), but I think such easymotion-isms are unidiomatic, and go against the philosophy of Leap. The intended use case of the leap-to-line example is linewise operations and selections. Anything more specific, jumping to the first non-blank character, to the end of the line, or empty lines can be achieved by the normal 2-char pattern mode (char-char, char-space, space-space, respectively), without the cognitive overhead of thinking about special kinds of motions and their idiosyncratic keymappings.