Include PHPCS path in `$PATH`. Install WP standards for PHPCS.

Before:

```bash
/srv/www/phpcs/scripts/phpcs --standard=CodeSniffer/Standards/WordPress/WordPress/ruleset.xml ./htdocs/wp-load.php
```

After:
```bash
phpcs --standard=WordPress ./htdocs/wp-load.php
```
Hmmmm. The previous worked for me (obvs) from inside the Vagrant, but I've got problems with the relative path:

```
vagrant@vvv:/srv/www/glow-blogs$ phpcs --config-set installed_paths CodeSniffer/Standards/WordPress/
vagrant@vvv:/srv/www/glow-blogs$ phpcs -i
PHP Fatal error:  Uncaught exception 'UnexpectedValueException' with message 'DirectoryIterator::__construct(CodeSniffer/Standards/WordPress/): failed to open dir: No such file or directory' in /srv/www/phpcs/CodeSniffer.php:1995
Stack trace:
#0 /srv/www/phpcs/CodeSniffer.php(1995): DirectoryIterator->__construct('CodeSniffer/Sta...')
#1 /srv/www/phpcs/CodeSniffer/CLI.php(870): PHP_CodeSniffer::getInstalledStandards()
#2 /srv/www/phpcs/CodeSniffer/CLI.php(246): PHP_CodeSniffer_CLI->printInstalledStandards()
#3 /srv/www/phpcs/CodeSniffer/CLI.php(213): PHP_CodeSniffer_CLI->processShortArgument('i', 1, Array)
#4 /srv/www/phpcs/CodeSniffer/CLI.php(526): PHP_CodeSniffer_CLI->getCommandLineValues()
#5 /srv/www/phpcs/scripts/phpcs(37): PHP_CodeSniffer_CLI->process()
#6 {main}
  thrown in /srv/www/phpcs/CodeSniffer.php on line 1995
```