Update Signal.signame doc [ci-skip]

* signal.c (sig_signame): [DOC] Add documentation in the case of
  return nil.  [Fix GH-1449]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@56280 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 3 insertions, 2 deletions

diff --git a/signal.c b/signal.c
index 32c7c2a099..8ebb6b9c61 100644
--- a/signal.c
+++ b/signal.c
@@ -238,9 +238,10 @@ signo2signm(int no)
 
 /*
  * call-seq:
- *     Signal.signame(signo)  ->  string
+ *     Signal.signame(signo)  ->  string or nil
  *
- *  convert signal number to signal name
+ *  Convert signal number to signal name.
+ *  Returns +nil+ if the signo is an invalid signal number.
  *
  *     Signal.trap("INT") { |signo| puts Signal.signame(signo) }
  *     Process.kill("INT", 0)