make documentation more accessible

[disassembler]

In trying to get the API documentation, the README references running npm run doc`. I ran this and it spits out a not very useful message:

> @ doc /home/sam/js-chain-libs
> jsdoc -c jsdoc.json pkg/js_chain_libs.js README.md -d docs

ERROR: Unable to find the source file or directory /home/sam/js-chain-libs/pkg/js_chain_libs.js
There are no input files to process.
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! @ doc: `jsdoc -c jsdoc.json pkg/js_chain_libs.js README.md -d docs`
npm ERR! Exit status 1
npm ERR! 
npm ERR! Failed at the @ doc script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.
npm WARN Local package.json exists, but node_modules missing, did you mean to install?

npm ERR! A complete log of this run can be found in:
npm ERR!     /home/sam/.npm/_logs/2019-09-25T17_40_49_506Z-debug.log

I then assumed maybe I need to build this first to read the documentation? SO I ran:

wasm-pack build
Error: No such file or directory (os error 2)

It would be nice to be able to view the documentation without going through hoops, and also for the documentation to have the right commands in it to get the documentation to build.