Merge to XFA: Describe required properties of public/ files with a README.
Original Review URL: https://codereview.chromium.org/1140833002
TBR=thestig@chromium.org
Review URL: https://codereview.chromium.org/1128863005
diff --git a/public/README b/public/README
new file mode 100644
index 0000000..b07d0f3
--- /dev/null
+++ b/public/README
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+public/ README
+
+The header files in this directory are the only ones that should ever be
+included by an embedder of PDFium. If there arises a need for functionality
+beyond what is present here, then a new API must be added here to provide it.
+
+These header files must be entirely contained in this directory; they must
+never include other header files from outside of it.
+
+These files must compile cleanly without warnings on both C and C++ compilers.
+
+Changes to these files must be carefully considered to avoid breaking
+compatibility.
