add gitattributes

this may be expanded

.gitattributes

@@ -0,0 +1,7 @@
+* annex.largefiles=largerthan=10MB
+
+
+*.md annex.largefiles=nothing
+*.py annex.largefiles=nothing
+*.r annex.largefiles=nothing
+*.rmd annex.largefiles=nothing