README.Debian: Describe where to find patches for a specific version

I think this is more useful than linking to the master branch.  Almost
no-one is running the packages from experimental.

debian/README.Debian

@@ -6,7 +6,9 @@ Patches
 Debian applies small changes to the kernel source. These are split up into
 separated patches addressing individual problems. Each of the patch files
 contains a description and mentions the author. The patches can be found
-at https://salsa.debian.org/kernel-team/linux/tree/master/debian/patches.
+in the source package or at
+https://sources.debian.org/src/linux/<version>/debian/patches/
+(with the package version substituted).
 
 Config Files
 ------------

debian/changelog

@@ -149,6 +149,7 @@ linux (4.18.7-1) UNRELEASED; urgency=medium
   * debian/{watch,bin/uscan-hook}: Drop uscan hook in favour of uupdate
   * debian/watch: Add options for signature validation
   * README.Debian: Update URLs that were pointing to Alioth
+  * README.Debian: Describe where to find patches for a specific version
 
   [ Salvatore Bonaccorso ]
   * mac80211: don't update the PM state of a peer upon a multicast frame