docs/devel: add b4 for patch retrieval

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Message-Id: <20241209183104.365796-4-pierrick.bouvier@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20250116160306.1709518-34-alex.bennee@linaro.org>

Author: pbo-linaro

docs/devel/submitting-a-patch.rst

@@ -433,6 +433,20 @@ For more details on how QEMU's stable process works, refer to the
 
 .. _participating_in_code_review:
 
+Retrieve an existing series
+---------------------------
+
+If you want to apply an existing series on top of your tree, you can simply use
+`b4 <https://github.com/mricon/b4>`__.
+
+::
+
+    b4 shazam $msg-id
+
+The message id is related to the patch series that has been sent to the mailing
+list. You need to retrieve the "Message-Id:" header from one of the patches. Any
+of them can be used and b4 will apply the whole series.
+
 Participating in Code Review
 ----------------------------