FPII-2034: DO NOT MERGE Update libpng to 1.6.20

DO NOT MERGE Update libpng to 1.6.20

BUG:23265085
Change-Id: I2fc2106965c789a54f04412e9c63a0901b0c1e71
(cherry picked from commit 0b39f202aaedd3029e4270d2af7d58ba6634f9cd)
diff --git a/README.version b/README.version
new file mode 100644
index 0000000..58890dd
--- /dev/null
+++ b/README.version
@@ -0,0 +1,3 @@
+URL: http://prdownloads.sourceforge.net/libpng/libpng-1.6.20.tar.gz?download
+Version: 1.6.20
+BugComponent: 87896