markdownlint: fix all warnings

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I0f8f7fbc23cb0113c093cad8a7d722054eac960a
diff --git a/README.md b/README.md
index ae2cef7..5f54515 100644
--- a/README.md
+++ b/README.md
@@ -14,7 +14,7 @@
 Multiple instances of `phosphor-certificate-manager` are usually run on the bmc
 to support management of different types of certificates.
 
-```
+```text
 Usage: ./phosphor-certificate-manager [options]
 Options:
     --help            Print this menu