updated readme

Author: xelatihy

README.md

@@ -141,6 +141,11 @@ target_link_libraries(myprogram PUBLIC fast_float)
 
 ```
 
+## Using as single header
+
+The script `amalgamate.py` may be used to generate a single header version of the library is so desired.
+Just run the script from the root directory of this repository. 
+You can customize the license type and output file is desired as described in the command line help.
 
 ## Credit