README: add more description

Move the README to README.md so Gerrit can render it; currently
Gerrit only renders files named exactly "README.md" (for example at
https://go.googlesource.com/go).

Add more links to the README explaining how to file issues,
how to submit code changes, where to download the code to and
how to get it. Hopefully this should help people who go to
https://go.googlesource.com/image or https://github.com/golang/image
figure out how to get started with development.

Change-Id: I390d4bd84c9fd7d0bd3f3f56f63ea8482d03a725
Reviewed-on: https://go-review.googlesource.com/49830
Reviewed-by: Kevin Burke <kev@inburke.com>
diff --git a/README b/README
deleted file mode 100644
index 4620380..0000000
--- a/README
+++ /dev/null
@@ -1,3 +0,0 @@
-This repository holds supplementary Go image libraries.
-
-To submit changes to this repository, see http://golang.org/doc/contribute.html.
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..0a312b4
--- /dev/null
+++ b/README.md
@@ -0,0 +1,17 @@
+# Go Images
+
+This repository holds supplementary Go image libraries.
+
+## Download/Install
+
+The easiest way to install is to run `go get -u golang.org/x/image`. You can
+also manually git clone the repository to `$GOPATH/src/golang.org/x/image`.
+
+## Report Issues / Send Patches
+
+This repository uses Gerrit for code changes. To learn how to submit changes to
+this repository, see https://golang.org/doc/contribute.html.
+
+The main issue tracker for the image repository is located at
+https://github.com/golang/go/issues. Prefix your issue with "x/image:" in the
+subject line, so it is easy to find.