rephrase following review

README.md

@@ -73,7 +73,7 @@ foo() = nothing
 # COV_EXCL_STOP
 ```
 
-To exclude a single line, add `COV_EXCL_LINE` anywhere:
+To exclude a single line, add `COV_EXCL_LINE` on that line:
 ```julia
 const a = 1  # COV_EXCL_LINE
 ```