Add README.md and .gitreview

Change-Id: Id5bb4e11871dde70a6b2b92ac1c3b5ef34a0ae62

.gitreview

+[gerrit]
+host=brainscales-r.kip.uni-heidelberg.de
+port=29418
+project=libnux
+defaultbranch=master
+defaultremote=review
+defaultrebase=0

README.md

+# Libraries for NUX Software
+
+* C-Runtime Support
+* Math Library
+* Vector Instruction Macros