Documentation: alter checkout --orphan description

The present text is a try to enhance description accuracy.  It is a
merge of the rewritten text made by native english speaker Chris Johnsen
and further changes of Junio.  It came from the last thread messages of
--orphan patch.

Signed-off-by: Erick Mattos <erick.mattos@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-checkout.txt

@@ -91,22 +91,29 @@ explicitly give a name with '-b' in such a case.
 	details.
 
 --orphan::
-	Create a new branch named <new_branch>, unparented to any other
+	Create a new 'orphan' branch, named <new_branch>, started from
-	branch.  The new branch you switch to does not have any commit
+	<start_point> and switch to it.  The first commit made on this
-	and after the first one it will become the root of a new history
+	new branch will have no parents and it will be the root of a new
-	completely unconnected from all the other branches.
+	history totally disconnected from all the other branches and
+	commits.
 +
-When you use "--orphan", the index and the working tree are kept intact.
+The index and the working tree are adjusted as if you had previously run
-This allows you to start a new history that records set of paths similar
+"git checkout <start_point>".  This allows you to start a new history
-to that of the start-point commit, which is useful when you want to keep
+that records a set of paths similar to <start_point> by easily running
-different branches for different audiences you are working to like when
+"git commit -a" to make the root commit.
-you have an open source and commercial versions of a software, for example.
 +
-If you want to start a disconnected history that records set of paths
+This can be useful when you want to publish the tree from a commit
-totally different from the original branch, you may want to first clear
+without exposing its full history. You might want to do this to publish
-the index and the working tree, by running "git rm -rf ." from the
+an open source branch of a project whose current tree is "clean", but
-top-level of the working tree, before preparing your files (by copying
+whose full history contains proprietary or otherwise encumbered bits of
-from elsewhere, extracting a tarball, etc.) in the working tree.
+code.
++
+If you want to start a disconnected history that records a set of paths
+that is totally different from the one of <start_point>, then you should
+clear the index and the working tree right after creating the orphan
+branch by running "git rm -rf ." from the top level of the working tree.
+Afterwards you will be ready to prepare your new files, repopulating the
+working tree, by copying them from elsewhere, extracting a tarball, etc.
 
 -m::
 --merge::