README outdated

[JordanPlayz158]

The development builds section is outdated at https://github.com/openfl/swf#development-builds

"
Go to the tools folder:

cd swf/tools

Tell haxe to build:

haxe build.hxml

"

The now correct actions would be

"
Go to the root directory of the cloned repository:

cd swf

Tell haxe to rebuild:

haxe rebuild.hxml

"

Note: I know this is something small but it is important to keep documentation up to date for people who are new to the libraries/frameworks and their tools