doc to explain how to update profile (#48)

Author: liamjm

README.md

@@ -51,6 +51,16 @@ Major Changes From Original Version
     implementation yet.
 
 
+Updating to new FIT SDK versions
+--------------------------------
+Download the latest SDK from http://www.thisisant.com/pages/products/fit-sdk
+
+Update the profile:
+```
+python3 scripts/generate_profile.py /path/to/fit_sdk.zip fitparse/profile.py
+```
+
+
 License
 -------