Add documentation for developers

[MichaelCurrin]

Hi, I recently came across in this project and am interested but found the docs experience limited, even for performing a few tasks to setup and run.

Fortunately I have experience with make and Go, so was able to figure some stuff out myself.

There is one item in docs on architecture.

[MichaelCurrin]

What I am looking for is something like this, as notes for developers working on the project:

• docs/installation.md

  # Installation
  
  ## Install system dependencies
   
  Install Go 1.16...
  
  (Install Node?)
  
  ## Clone
  
  Clone the repo:
  
      git clone git@github.com:evanw/esbuild.git.
  

• docs/usage.md

  # Usage
  
  ## Tests
  
      make test
  
  ## Build
  
  Create binary in the current directory.
  
      make
  
  Test it:
  
      ./esbuild -h
  

Maybe some examples of how to run that command against some sample scripts to verify it is working.

That was from a Go perspective - maybe add something for JS developers - like how to Install Node and how to run and test some scripts in this project.

See also my generic Go project template for reference - it uses make heavily. https://github.com/MichaelCurrin/go-project-template/tree/main/docs