Add disclaimer
Add disclaimer

As per feedback from the vote thread at IPMC for 0.8.1 release, and guideline here:
http://incubator.apache.org/guides/branding.html#disclaimers

Author: Felix Cheung <felixcheung_m@hotmail.com>

Closes #62 from felixcheung/disclaimer.

manuzhang/incubator-gearpump,manuzhang/incubator-gearpump,manuzhang/incubator-gearpump,manuzhang/incubator-gearpump,manuzhang/incubator-gearpump