README.md: Point to CI for getting a PDF

Author: jrtc27

README.md

@@ -3,3 +3,6 @@ help developers working with pure-capability C/C++ understand the benefits
 that it brings, any code adaptations they might need to make, and how to
 interpret new compiler warnings and errors that arise with pure-capability
 code.
+
+For a pre-typeset PDF version of this document, please find the latest CI run at
+https://github.com/CTSRD-CHERI/cheri-c-programming/actions.