[dsymutil][doc] Improve wording in manpage and rename file.

 - Improve wording
 - Rename llvm-dsymutil to dsymutil
 - Name -arch=<arch> argument

Differential revision: https://reviews.llvm.org/D39561

llvm-svn: 317226
diff --git a/llvm/docs/CommandGuide/llvm-dwarfdump.rst b/llvm/docs/CommandGuide/llvm-dwarfdump.rst
index 4e77915..a3b6266 100644
--- a/llvm/docs/CommandGuide/llvm-dwarfdump.rst
+++ b/llvm/docs/CommandGuide/llvm-dwarfdump.rst
@@ -139,4 +139,4 @@
 SEE ALSO
 --------
 
-:manpage:`llvm-dsymutil(1)`
+:manpage:`dsymutil(1)`