[llvm-install-name-tool] Adds docs for llvm-install-name-tool

Adding documentation for llvm-install-name-tool.

Reviewed by smeenai, Ktwu

Differential Revision: https://reviews.llvm.org/D81944
diff --git a/llvm/docs/CommandGuide/index.rst b/llvm/docs/CommandGuide/index.rst
index d13c2a0..2dae12b 100644
--- a/llvm/docs/CommandGuide/index.rst
+++ b/llvm/docs/CommandGuide/index.rst
@@ -44,6 +44,7 @@
    llvm-addr2line
    llvm-ar
    llvm-cxxfilt
+   llvm-install-name-tool
    llvm-nm
    llvm-objcopy
    llvm-objdump