[llvm-objdump] Add --no-print-imm-hex to the command guide

The option --no-print-imm-hex was not included in the command guide for
llvm-objdump but appears in the help text. This commit adds it to the
command guide.

Differential Revision: https://reviews.llvm.org/D104717

llvm/docs/CommandGuide/llvm-objdump.rst

@@ -169,6 +169,10 @@ OPTIONS
 
   When disassembling, do not print leading addresses.
 
+.. option:: --no-print-imm-hex
+
+  Do not use hex format for immediate values in disassembly output (default).
+
 .. option:: --no-show-raw-insn
 
   When disassembling, do not print the raw bytes of each instruction.