[13] RFR: JDK-8218174: Add missing license file for Mesa header files

[Kevin Rushforth]

Phil,

Please review the following simple fix to add a missing *.md file for 
the Mesa3D header files:

https://bugs.openjdk.java.net/browse/JDK-8218174
http://cr.openjdk.java.net/~kcr/8218174/webrev/

-- Kevin