Release process: better specify requirements.

wiki/src/contribute/release_process/perl5lib.mdwn

@@ -73,7 +73,8 @@ Commit `debian/changelog`:
 Git-Dch: Ignore
 "
 
-Build a Debian package (use a Stretch/amd64 chroot):
+Build a Debian package (use a Stretch/amd64 chroot with `stretch-backports`
+enabled):
 
     gbp buildpackage
 

wiki/src/contribute/release_process/persistence-setup.mdwn

@@ -7,7 +7,7 @@ Pre-requisites
 
 * a Debian Stretch (or newer) system
 * Tails' `devel` APT suite enabled
-* the right version of the `tails-perl5lib` package installed
+* the latest version of the `tails-perl5lib` package installed
 
 Install build and test dependencies
 ===================================
@@ -80,9 +80,9 @@ Commit `debian/changelog`:
 Git-Dch: Ignore
 "
 
-Build a Debian package (use a Stretch/amd64 chroot, that
-has either tails-perl5lib installed, or the Tails APT repository
-configured):
+Build a Debian package (use a Stretch/amd64 chroot, that has
+`stretch-backports` enabled and on top of that: either tails-perl5lib
+installed or the Tails APT repository configured):
 
     gbp buildpackage
 

wiki/src/contribute/release_process/tails-iuk.mdwn

@@ -109,9 +109,9 @@ Commit `debian/changelog`:
 Git-Dch: Ignore
 "
 
-Build a Debian package (use a Stretch chroot with the right version of
-`tails-perl5lib` installed), add a signed tag to the repository and
-push the changes:
+Build a Debian package (use a Stretch/amd64 chroot, that has
+`stretch-backports` enabled and on top of that: either tails-perl5lib
+installed or the Tails APT repository configured):
 
     gbp buildpackage && \
     gbp buildpackage --git-tag-only --git-sign-tags && \