go modules support

diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..eec1581
--- /dev/null
+++ b/go.mod

@@ -0,0 +1,7 @@
+module gopkg.in/src-d/go-billy.v4
+
+require (
+	github.com/kr/pretty v0.1.0 // indirect
+	golang.org/x/sys v0.0.0-20180903190138-2b024373dcd9
+	gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127
+)

diff --git a/go.sum b/go.sum
new file mode 100644
index 0000000..aa96620
--- /dev/null
+++ b/go.sum

@@ -0,0 +1,9 @@
+github.com/kr/pretty v0.1.0 h1:L/CwN0zerZDmRFUapSPitk6f+Q3+0za1rQkzVuMiMFI=
+github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORNo=
+github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
+github.com/kr/text v0.1.0 h1:45sCR5RtlFHMR4UwH9sdQ5TC8v0qDQCHnXt+kaKSTVE=
+github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
+golang.org/x/sys v0.0.0-20180903190138-2b024373dcd9 h1:lkiLiLBHGoH3XnqSLUIaBsilGMUjI+Uy2Xu2JLUtTas=
+golang.org/x/sys v0.0.0-20180903190138-2b024373dcd9/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127 h1:qIbj1fsPNlZgppZ+VLlY7N33q108Sa+fhmuc+sWQYwY=
+gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=