[llvm-readobj] Add -elf-section-groups option

Adds a way to inspect SHT_GROUP sections in ELF objects.
Displays signature, member sections of these sections.

Differential revision: http://reviews.llvm.org/D16555

llvm-svn: 258845
diff --git a/llvm/docs/CommandGuide/llvm-readobj.rst b/llvm/docs/CommandGuide/llvm-readobj.rst
index b1918b5..417fcd0 100644
--- a/llvm/docs/CommandGuide/llvm-readobj.rst
+++ b/llvm/docs/CommandGuide/llvm-readobj.rst
@@ -80,6 +80,10 @@
 
  Display the ELF program headers (only for ELF object files).
 
+.. option:: -elf-section-groups, -g
+
+ Display section groups (only for ELF object files).
+
 EXIT STATUS
 -----------