Document VCS fields
Uses Developers's Reference §6.2.5 for inspiration.
Closes: #654958
[jrnieder@gmail.com:
- declared repositories should be publicly accessible
- Vcs-Browser should point to a webapp
- Vcs-<system> should use the version control system's conventional syntax
- if multiple branches are used for packaging (e.g., "stable",
"testing", "sid"), any one of them will do
- for Vcs-Git, "-b <branch>" can be omitted when the intended branch is the
default branch
- list some Vcs-<foo> fields by name in the lists in §5.2 and §5.4
- declared repositories track development of the Debian source
package, not just the upstream code
- Vcs-Browser can be a web interface using any protocol (e.g., HTTPS
is fine)
- picking a good branch is optional
Thanks to Russ Allbery for several improvements to the text.]