Add chapters about strings, bytes, runes and characters

[Jay54520]

I am still confused with strings, bytes, runes and characters in Go after reading Strings, bytes, runes and characters in Go. Could you consider add some chapters about them?

And the requirement could be "Replace all spaces in a String with ‘%20’".

[lshaowei18]

Hi Chris, I would like to help out with this but I am new to open source projects. What kind of help do you need?

[gypsydave5]

Would be awesome if it could reference Rob and Ken's work on UTF-8 https://www.cl.cam.ac.uk/~mgk25/ucs/utf-8-history.txt

[danish-parvez]

A reference to this would be good for an introduction!