user-manual: fix discussion of default clone

The name "master" isn't actually quite so special.  Also, fix some bad
grammar.

Signed-off-by: "J. Bruce Fields" <bfields@citi.umich.edu>
Signed-off-by: Junio C Hamano <junkio@cox.net>

Documentation/user-manual.txt

@@ -298,9 +298,9 @@ $ git branch
 * master
 ------------------------------------------------
 
-A freshly cloned repository contains a single branch head, named
-"master", and working directory is initialized to the state of
-the project referred to by "master".
+A freshly cloned repository contains a single branch head, by default
+named "master", with the working directory initialized to the state of
+the project referred to by that branch head.
 
 Most projects also use <<def_tag,tags>>.  Tags, like heads, are
 references into the project's history, and can be listed using the