Enable package auto-discovery.

[woodspire]

Further MR will be done related to this.

• Add bootstrap/cache folder in laravel-zero/foundation
• It seems it's required by the auto-discovery system. laravel-zero#470
• Rework documentation to install Tinker
• With package auto-discovery, only one command is required to install … docs#36

To disable this feature, simply add this to each project composer.json:

"extra": {
"laravel": {
"dont-discover": [
"*"
]
}
},

[nunomaduro]

This is a breaking change that I don't think is worth at the moment.