Merge pull request #3 from SKY-13th/hotfix/Fix_system_related_dependencies_issue

Fix system related dependencies issue

README.md

@@ -1,7 +1,13 @@
 # DerelictVulkan
-Vulkan api bindings
+Dynamic Vulkan api bindings
 
 Don't expect it to work until version 1.0.0
 
-Currently only _Windows_ is supported. 
-Feel free to make pull request for other OSes.
+Currently only __Windows__ and __Posix__(__Xlib__, __XCB__) is supported.
+Feel free to make pull request for other OSes.
+
+On __Posix__ to use __Xlib__ or/and __XCB__ specific functionality:
+- Add required library to your dependencies list
+- Add related version flag(s):
+  - **VK_USE_PLATFORM_XLIB_KHR**
+  - **VK_USE_PLATFORM_XCB_KHR**

dub.json

@@ -8,7 +8,7 @@
 	"targetType": "library",
 	"dependencies": {
 		"derelict-util" : ">=1.0.0",
-		"xlib-d": "~>0.1.1",
-		"xcb-d": "~>2.1.0+1.11.1"
+		"xlib-d": { "version": "~>0.1.1", "optional": true },
+		"xcb-d" : { "version": "~>2.1.0+1.11.1", "optional": true }
 	}
 }