Add README.md code block insertion from files

[gaand]

So all code is subject to linters, etc.

[MicFin]

As an example, the https://github.com/ga-wdi-boston/js (after 018/master is merged) talk utilizes the new add-code-block script. To include the snippets in grunt nag, it should be added to paths.json potentially as shown below.

{
  "src": {
    "all": [
      "bin/**/*.js",
      "lib/**/*.js",
      "spec/**/*.spec.js",
      "snippets/**/*.js"
    ],
    "spec": [
      "spec/**/*.spec.js"
    ],
    "lib": [
      "lib/**/*.js"
    ],
    "snippets": [
      "snippets/**/*.js"
    ]
  },

  "grunt": {
    "all": [
      "Gruntfile.js",
      "grunt/*.js"
    ]
  },

  "json": {
    "all": [
      "lib/**/*.json",
      "spec/**/*.json",
      "grunt/*.json",
      "snippets/**/*.json"
    ]
  }
}