Increase upload_max_filesize via Forge

Updating since this is the first search engine result for a search on this topic:

Forge now has a built-in setting you can update by going to the server details page and then clicking on PHP from the menu on the left. You'll see a form to change the max file size.

I was missing a piece. Here's the whole answer.

Nginx Configuration

Add the following line to http or server or location context to increase the size limit in nginx.conf:

# set client body size to 20M #
client_max_body_size 20M;

PHP Configuration

Edit php.ini and set the following directives:

;This sets the maximum amount of memory in bytes that a script is allowed to allocate
memory_limit = 256M

;The maximum size of an uploaded file.
upload_max_filesize = 20M

;Sets max size of post data allowed. This setting also affects file upload. To upload large files, this value must be larger than upload_max_filesize
post_max_size = 30M

Source: http://www.cyberciti.biz/faq/linux-unix-bsd-nginx-413-request-entity-too-large/