README: Point at README.OE-Core

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

diff --git a/README.md b/README.md
new file mode 120000 (symlink)
index 0000000..4d7e9e8
--- /dev/null
+++ b/README.md
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+README.OE-Core.md
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