We're about to extend our documentation to recommend b4 for sending
patch series ot the mailing list. Prepare for this by introducing a b4
configuration so that the tool knows to honor our preferences. For now,
this configuration does two things:

  - It configures "send-same-thread = shallow", which tells b4 to always
    send subsequent versions of the same patch series as a reply to the
    cover letter of the first version.

  - It configures "prep-cover-template", which tells b4 to use a custom
    template for the cover letter. The most important change compared to
    the default template is that our custom template also includes a
    range-diff.

There's potentially more things that we may want to configure going
forward, like for example auto-configuration of folks to Cc on certain
patches. But these two tweaks feel like a good place to start.

Signed-off-by: Patrick Steinhardt <redacted>
---
 .b4-config         |  3 +++
 .b4-cover-template | 11 +++++++++++
 2 files changed, 14 insertions(+)

diff --git a/.b4-config b/.b4-config
new file mode 100644
index 0000000000..14124728ce
--- /dev/null
+++ b/.b4-config

@@ -0,0 +1,3 @@
+[b4]
+send-same-thread = shallow
+prep-cover-template = ./.b4-cover-template

diff --git a/.b4-cover-template b/.b4-cover-template
new file mode 100644
index 0000000000..ab864933b5
--- /dev/null
+++ b/.b4-cover-template

@@ -0,0 +1,11 @@
+${cover}
+
+---
+${shortlog}
+
+${diffstat}
+
+${range_diff}
+---
+base-commit: ${base_commit}
+${prerequisites}

-- 
2.54.0.1064.gd145956f57.dirty