Add hw req. and using macros

Author: trdtnguyen

README.md

@@ -24,3 +24,13 @@ $ scons core -j40
 ```
 
 See [docs/building.md](docs/building.md) for more detail
+
+### Hardware requirements
++ Samsung 840 Pro - With the modified firmware supports Multi-streamed technique. OR
++ Samsung [PM953 2.5" NVMe PCIe](https://www.samsung.com/us/dell/pdfs/samsung_flyer_PM953_v2.pdf)
+
+### Using Macros:
+
+`TDN_TRIM4`: the TRIM command optimization. Save replaced ranges in the inner data structure. When the number of discard ranges reaches a threshold, invoke the __trim_ranges() thread.
+
+`TDN_TRIM4_2`: similar with `TDN_TRIM4`, differences is saving discard ranges instead of replaced ranges