Fixes broken link to Ruby Cells.

Now links to GitHub project page for the gem.
Merge pull request #1623 from alecho/patch-2

Fixes broken link to Ruby Cells.
Fix typo
Add notes on finder option added in cakephp/cakephp#4342
Removed notices about ``--stderr``

May be I missunderstood this, but acording to @lorenzo

https://github.com/cakephp/cakephp/pull/3521#issue-33758906

> With this merged, we have no longer need for running tests with --stderr and we can safely use phpunit 4.1
Fixed broken link to PHP's json_encode
Fix typo.

Fixes #1627
wrong method name in needsPasswordRehash example

loginProvider() does not exists
Merge pull request #1628 from stefanozoffoli/patch-1

wrong method name in needsPasswordRehash example
Improved commas and consistency
Some improvements to the getting started section
src folder with small S in title
Missing 'the'
Added info about the logs folder
3.0-fixes
Merge pull request #1632 from dereuromark/3.0-fixes

3.0-fixes
Merge pull request #1626 from cakephp/association-finder

Add notes on finder option added in cakephp/cakephp#4342
Merge pull request #1630 from cakephp/3.0-getting-started-improved

Some improvements to the getting started section
top level directory correction
minor correction

add [app-name] to composer comand