Created Performance Tips (markdown)

Performance-Tips.md

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+# Draw commands
+
+The less draw commands, the better the performance is.
+
+One drawing function like `DrawImage` or `Fill` is treated as one (internal) draw command, but there is an exception. The two or more successive commands are treated as one draw command when
+
+* All functions are `DrawImage`
+* All the render targets are same
+* All the render sources are same
+* All the color matrices are same
+* All the composite modes are same
+
+examples/sprites is a good example to draw > 10000 sprites with one draw commands.