clients.md: fix headers

"##Abc##" is not a valid syntax. Changed to header level 2.

Signed-off-by: Nan Zhou <nanzhoumails@gmail.com>
Change-Id: I1c52540bd741a65e8fa7d72237bb43a59d120b06
diff --git a/CLIENTS.md b/CLIENTS.md
index 7379599..010be31 100644
--- a/CLIENTS.md
+++ b/CLIENTS.md
@@ -11,7 +11,7 @@
 limitations in the testing tools behavior within bmcweb to make the tools pass,
 regardless of whether there is user impact.
 
-##Tests##
+## Tests
 
 Redfish-Service-Validator: A tool to verify through GET requests that bmcweb
 properly implements the Redfish schemas in the responded Resource.
@@ -46,7 +46,7 @@
 Status: Unknown
 
 
-##Clients##
+## Clients
 
 fwupd: Is a client implementation that allows updating firmware components in a
 generic way, and includes redfish as one of its plugins.