d/README.source: Addings some information about source

debian/README.source

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+This package is maintained with git-buildpackage(1). It follows DEP-14 for
+branch naming (e.g. using debian/master for the current version in Debian
+unstable due Debian Python team policy).
+
+It uses pristine-tar(1) to store enough information in git to generate bit
+identical tarballs when building the package without having downloaded an
+upstream tarball first.
+
+When working with patches it is recommended to use "gbp pq import" to import
+the patches, modify the source and then use "gbp pq export --commit" to commit
+the modifications.
+
+The changelog is generated using "gbp dch" so if you submit any changes don't
+bother to add changelog entries but rather provide a nice git commit message
+that can then end up in the changelog.
+
+It is recommended to build the package with pbuilder using:
+
+    gbp buildpackage --git-pbuilder
+
+For information on how to set up a pbuilder environment see the git-pbuilder(1)
+manpage. In short:
+
+    DIST=sid git-pbuilder create
+    gbp clone https://salsa.debian.org/python-team/packages/phython-click.git
+    cd python-click
+    gbp buildpackage --git-pbuilder
+
+ -- Carsten Schoenert <c.schoenert@t-online>  Wed, 30 Nov 2022 10:56:00 +0100