watchman installation should be included in the README instructions

[eyalliebermann]

The README instructs new users to clone install and start. This doesn't work for those of us who have not installed watchman on their machine

Expected Behavior

I think before the npm install, npm start phase users should be advised to verify they have watch do following the following link

Actual Behavior

Steps to Reproduce

Just follow the instructions on the current README file on a machine with no watchman you would see the following:

relay-fullstack git:(master) npm start

> relay-fullstack@1.0.0 start /Users/eyalliebermann/relay-fullstack
> nodemon --watch server/data/**/*.js --exec "npm run update && npm run start-sub-task"

[nodemon] 1.11.0
[nodemon] to restart at any time, enter `rs`
[nodemon] watching: server/data/**/*.js
[nodemon] starting `npm run update && npm run start-sub-task`

> relay-fullstack@1.0.0 update /Users/eyalliebermann/relay-fullstack
> babel-node server/utils/updateSchema.js && npm run relay

Schema has been regenerated

> relay-fullstack@1.0.0 relay /Users/eyalliebermann/relay-fullstack
> relay-compiler --src ./client --schema server/data/schema.graphql

HINT: pass --watch to keep watching for changes.
Watchman:  Watchman was not found in PATH.  See https://facebook.github.io/watchman/docs/install.html for installation
 instructions
events.js:182
      throw er; // Unhandled 'error' event
      ^

Error: Watchman was not found in PATH.  See https://facebook.github.io/watchman/docs/install.html for installation ins
tructions
    at exports._errnoException (util.js:1026:11)
    at Process.ChildProcess._handle.onexit (internal/child_process.js:189:19)
    at onErrorNT (internal/child_process.js:366:16)
    at _combinedTickCallback (internal/process/next_tick.js:102:11)
    at process._tickCallback (internal/process/next_tick.js:161:9)
    at Function.Module.runMain (module.js:607:11)
    at startup (bootstrap_node.js:158:16)
    at bootstrap_node.js:575:3
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! relay-fullstack@1.0.0 relay: `relay-compiler --src ./client --schema server/data/schema.graphql`
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the relay-fullstack@1.0.0 relay script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR!     /Users/eyalliebermann/.npm/_logs/2017-07-10T10_35_59_263Z-debug.log
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! relay-fullstack@1.0.0 update: `babel-node server/utils/updateSchema.js && npm run relay`
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the relay-fullstack@1.0.0 update script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR!     /Users/eyalliebermann/.npm/_logs/2017-07-10T10_35_59_296Z-debug.log
[nodemon] app crashed - waiting for file changes before starting...
^C%
➜  relay-fullstack git:(master) brew update

[lvarayut]

Thanks @eyalliebermann for the suggestion. You're absolutely right, we need to add that to the README. A PR would be very welcomed :)

[lvarayut]

Added in https://github.com/lvarayut/relay-fullstack/commit/67d9b312b0dc9c33af96cbd44eba5ae639c3bcc7