In 6218a99a3a the Makefile was updated to
use the new `pkg-config` method for including Hyprland soucres, however
this commit didn't update the README instructions, which did change a
bit.
The most notable change is that exporting `HYPRLAND_HEADERS` is no
longer necessary, and the updated required Hyprland commit for the
plugin.
This commit also updates the hyprload instructions.
Hyprland has recently changed the way plugins recognize the hyprland
headers, moving from directly including the paths with -I option to
automatically generating the cflags with `pkg-config --cflags hyprland`.
This change means that compilation attempts using the direct include
option will start to fail with newer versions of hyprland, which now
uses /usr/local/include for it's headers after `make pluginenv`.
This commit migrates the original system to respect this change,
modifying Makefile, and with it, the include paths for hyprland headers,
which are now prefixed with hyprland/.