The READMEs directory contains files that describe new features, software incompatibilities, bugs, and information that was discovered after the manuals were printed. The location of this directory depends on where your software was installed.
The READMEs in a standard install would appear in: /opt/SUNWspro/READMEs/
The READMEs for all compilers are easily accessed by the --xhelp=readme command-line option. For example, CC -xhelp=readme displays the C++ README file directly.