[docs] [tblgen] clarify that code fragments are just string literals

Fun fact: looking at the TableGen code (around TGParser.cpp:1166), the
only difference in handling is that adjacent regular string literals are
concatenated in the parser.

llvm-svn: 201035
diff --git a/llvm/docs/TableGenFundamentals.rst b/llvm/docs/TableGenFundamentals.rst
index 5d529c3..8f3d07c 100644
--- a/llvm/docs/TableGenFundamentals.rst
+++ b/llvm/docs/TableGenFundamentals.rst
@@ -289,7 +289,7 @@
     string value
 
 ``[{ ... }]``
-    code fragment
+    usually called a "code fragment", but is just a multiline string literal
 
 ``[ X, Y, Z ]<type>``
     list value.  <type> is the type of the list element and is usually optional.