Writer options and FileWriter example in Readme

[nfriedly]

• Documents the params & options for Writer and FileWriter
• Adds a FileWriter example with mic

I omitted the format option from Writer because it looks like it doesn't support any other options.

[nfriedly]

Oh, nice, I'll have to try that out!

Go ahead and switch the example to line-in if you want, I won't take any offense.

[LinusU]

sorry for the delay