DOC: clarify the agent-check status line syntax

Nick Ramirez reported that the wording is confusing and lets one think
that the CR or LF are both optional, which is not the case (either is
optional). Let's reformulate this.
diff --git a/doc/configuration.txt b/doc/configuration.txt
index fea7a19..46182cb 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -11425,9 +11425,9 @@
 agent-check
   Enable an auxiliary agent check which is run independently of a regular
   health check. An agent health check is performed by making a TCP connection
-  to the port set by the "agent-port" parameter and reading an ASCII string.
-  The string is made of a series of words delimited by spaces, tabs or commas
-  in any order, optionally terminated by '\r' and/or '\n', each consisting of :
+  to the port set by the "agent-port" parameter and reading an ASCII string
+  terminated by the first '\r' or '\n' met. The string is made of a series of
+  words delimited by spaces, tabs or commas in any order, each consisting of :
 
   - An ASCII representation of a positive integer percentage, e.g. "75%".
     Values in this format will set the weight proportional to the initial