Add info about StringReader for #50

[vishalsodani]

No description provided.

[mark-i-m]

Thanks! Would it be possible to add a bit more information? How does it help with lexing?

[vishalsodani]

@mark-i-m I don't have much understanding how the compiler works. I found this walkthrough. Should I add this line

This is the interface which consumes the raw source input and converts it to a series of Tokens & Spans in a TokenStream.

[mark-i-m]

@vishalsodani I think that looks good. Perhaps we could modify it as such:

This is the lexer used during parsing. It consumes characters from the raw source code being compiled and produces a series of tokens for use by the rest of the parser.

[mark-i-m]

Thanks!