Added READMEs for some library modules which didn't have them

libcdr/README

+Library parsing the Corel cdr documents.
+
+I couldn't find an upstream for this library - although I did only try a primitive Google search.

libcmis/README

+A C++ client library for the CMIS interface.
+
+From:
+[http://sourceforge.net/projects/libcmis/]
+
+Wikipedia (CMIS):
+Content Management Interoperability Services (CMIS) is an open standard that defines an
+abstraction layer for controlling diverse document management systems and repositories using web protocols.

libcroco/README

+A general CSS parsing and manipulation library written in C for the GNOME project.
+
+From:
+[https://launchpad.net/libcroco]

libgsf/README

+A simple i/o library that can read and write common file types and handle structured formats that provide file-system-in-a-file semantics.
+
+From:
+[http://www.gnome.org/projects/libgsf]

libpng/README

+libpng is the official PNG reference library, from [http://www.libpng.org/]

librsvg/README

+Rapid Rendering of SVG files to screen or to other more conventional filetypes, such as JPEG and PNG.
+
+From:
+[http://librsvg.sourceforge.net/]

libvisio/README

+Libvisio is library providing ability to interpret and import visio diagrams into various applications.
+
+See also:
+[http://www.freedesktop.org/wiki/Software/libvisio]