update markdown/help header format

Since gitiles recommends using # headers over ---/=== underlines,
change the manifest-format.md over and all our help texts.

Change-Id: I96391d41fba769e9f26870d497cf7cf01c8d8ab3
diff --git a/subcmds/upload.py b/subcmds/upload.py
index fdc7e28..c1f5c0f 100644
--- a/subcmds/upload.py
+++ b/subcmds/upload.py
@@ -78,8 +78,7 @@
 new users.  Users passed as --reviewers must already be registered
 with the code review system, or the upload will fail.
 
-Configuration
--------------
+# Configuration
 
 review.URL.autoupload:
 
@@ -126,8 +125,7 @@
 of the -t option to the repo command. If unset or set to "false" then
 repo will make use of only the command line option.
 
-References
-----------
+# References
 
 Gerrit Code Review:  http://code.google.com/p/gerrit/