Update README.md

Author: WikiBox

README.md

@@ -1,2 +1,21 @@
 # SD
-String dictionary with front coding compression
+C++ String dictionary with front coding compression and serialization
+
+sd is a C++ class implementing a compressed string dictionary. The class provides fast add, locate and 
+extract using front coding compression. Front coding compression means that common prefixes are compressed. This makes this string dictionary suitable for compact storage and fast access to a huge amount of strings like URL:s or file paths. Using sd it may be possible to hold a complete dictionary in RAM instead of having to use slower disk-based storage.
+
+Note: 
+* Strings must be added in strict ascending lexicographic order. 
+* Strings are stored as raw bytes, but '\0' cant't be used in a string because that char is used as string terminator inside the data structure.
+* BUCKET_SIZE may be changed to shift the trade-off between compression level and speed of access. Big BUCKET_SIZE means higher compression but slower access. Sane values are between 16 and 2048.
+ 
+This software is simplified version of StringDictionaryPFC from libCSD:
+```
+==========================================================================
+  "Compressed String Dictionaries"
+  Nieves R. Brisaboa, Rodrigo Cánovas, Francisco Claude, 
+  Miguel A. Martínez-Prieto, and Gonzalo Navarro
+  10th Symposium on Experimental Algorithms (SEA'2011), p.136-147, 2011.
+==========================================================================
+```
+See: https://github.com/migumar2/libCSD