[docs] Add missing features for the x86-64 ELF backend.

llvm-svn: 203313
diff --git a/lld/docs/open_projects.rst b/lld/docs/open_projects.rst
index e7b631b..386f51e 100644
--- a/lld/docs/open_projects.rst
+++ b/lld/docs/open_projects.rst
@@ -5,6 +5,7 @@
 
 .. include:: ../include/lld/Core/TODO.txt
 .. include:: ../lib/Core/TODO.txt
+.. include:: ../lib/ReaderWriter/ELF/X86_64/TODO.rst
 .. include:: ../tools/lld/TODO.txt
 
 Documentation TODOs