Fix some typos in gn's documentation for "copy".

tools/gn/functions_target.cc

Index: tools/gn/functions_target.cc
diff --git a/tools/gn/functions_target.cc b/tools/gn/functions_target.cc
index 45e685965371f77579b2e25c4a4e0ebd817f3eec..5c30fb9bc08c043103a1c86b426b124d682231a9 100644
--- a/tools/gn/functions_target.cc
+++ b/tools/gn/functions_target.cc
@@ -252,15 +252,16 @@ const char kCopy_Help[] =
     "  reference the output or generated intermediate file directories,\n"
     "  respectively.\n"
     "\n"
-    "  Both \"sources\" and \"outputs\" must be specified. Sources can\n"
+    "  Both \"sources\" and \"outputs\" must be specified. Sources can "
+    "include\n"
     "  as many files as you want, but there can only be one item in the\n"
     "  outputs list (plural is used for the name for consistency with\n"
     "  other target types).\n"
     "\n"
     "  If there is more than one source file, your output name should specify\n"
-    "  a mapping from each source files to output file names using source\n"
+    "  a mapping from each source file to an output file name using source\n"
     "  expansion (see \"gn help source_expansion\"). The placeholders will\n"
-    "  will look like \"{{source_name_part}}\", for example.\n"
+    "  look like \"{{source_name_part}}\", for example.\n"
     "\n"
     "Examples\n"
     "\n"