[libcxx][docs] Clearer mark up for --param

Summary:
When I read this on the website it looks like the `--` in the used font turns
into an em dash. I updated this with inline literal mark up so the `--` will
remain obvious.

Reviewers: EricWF, #libc!

Subscribers: libcxx-commits

Tags: #libc

Differential Revision: https://reviews.llvm.org/D78405

Cr-Mirrored-From: https://chromium.googlesource.com/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 33ad38a925aa5120a547ed16f0c2a6d07f16e8e5
diff --git a/docs/TestingLibcxx.rst b/docs/TestingLibcxx.rst
index b70cf2e..26dfefc 100644
--- a/docs/TestingLibcxx.rst
+++ b/docs/TestingLibcxx.rst
@@ -102,9 +102,10 @@
 Command Line Options
 --------------------
 
-To use these options you pass them on the LIT command line as --param NAME or
---param NAME=VALUE. Some options have default values specified during CMake's
-configuration. Passing the option on the command line will override the default.
+To use these options you pass them on the LIT command line as ``--param NAME``
+or ``--param NAME=VALUE``. Some options have default values specified during
+CMake's configuration. Passing the option on the command line will override the
+default.
 
 .. program:: lit