Update README.md

shader_deblocking/README.md

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 Many variations and optimizations of this basic idea are possible. *Now shader engineers can directly impact memory consumption.* The better your deblocking shaders are tuned or your specific content, the bigger the ASTC block size you can ship. ASTC texture deblocking pixel shader engineering is now a memory optimization skill. 
 
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+## Performance
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+The deblocking shader itself can be put inside a dynamic `if` conditional, so the extra ALU/texture ops only kick in near block edges (which are the minority of samples at ASTC 12x12). The extra sample taps are spatially always near the center sample, so they'll hit the texture cache most of the time. In texture bandwidth bound rendering scenarios (quite common on mobile platforms), the extra ALU ops for deblocking likely come for "free".
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 ## Screenshots - ASTC 12x12 Block Size