licenses: Add W3C license.

* gnu/license.scm (w3c): New variable.

guix/licenses.scm

@@ -87,6 +87,7 @@
             tcl/tk
             unlicense
             vim
+            w3c
             x11 x11-style
             zpl2.1
             zlib
@@ -578,6 +579,11 @@ at URI, which may be a file:// URI pointing the package's tree."
            "https://unlicense.org/"
            "https://www.gnu.org/licenses/license-list.html#Unlicense"))
 
+(define w3c
+  (license "W3C Software Notice and License"
+           "https://directory.fsf.org/wiki/License:W3C_31Dec2002"
+           "https://www.gnu.org/licenses/license-list.en.html#W3C"))
+
 (define wtfpl2
   (license "WTFPL 2"
            "http://www.wtfpl.net"