Edits to segwit send docs
Edits to segwit send docs

- I added an import to line 242 just so it's clear that those are built in utils rather than your custom helper. easier to write in one line with es6 imports but maybe you don't want it like that since it might not work out of the box? 
- line 259 - What's "BE" and "LE"?
- line ~350- where does `spend1` come from? 
- for the code block at lines 363-379, this not code you're using right? just what was being done before? If so, maybe we don't have that code block (i.e. better to only show code for a section if that is what you want to be doing)
- for the last section where you use `getNestedAddress`, it looks like bcoin will actually automatically do a check for you when using the default (`getAddress`, etc.) so it's not really necessary to use a different method is it? If they do the same thing maybe make a note at least that you can actually use `getAddress` in either case but you're using the specialized one to make it more clear.
bcoin-org/bcoin-org.github.io,bcoin-org/bcoin-org.github.io,bcoin-org/bcoin-org.github.io,bcoin-org/bcoin-org.github.io