docs(commit-style): add a message about lower case

Although not clearly mentioned in Conventional Commits spec[1], the
first letter of the description must be lower case to pass the
commitlint check. This is described in the test for subject case[2].

[1]: https://www.conventionalcommits.org/en/v1.0.0/#specification
[2]: https://github.com/conventional-changelog/commitlint/tree/master/%40commitlint/config-conventional#subject-case

Signed-off-by: Yann Gautier <yann.gautier@st.com>
Change-Id: I862382452784319a9ae659a70e49a61d79de6ed2
diff --git a/docs/process/commit-style.rst b/docs/process/commit-style.rst
index c287599..97b4b44 100644
--- a/docs/process/commit-style.rst
+++ b/docs/process/commit-style.rst
@@ -36,6 +36,9 @@
 
     [optional footer(s)]
 
+Note that the type, the scope and the first letter of the description (also
+called subject by the commitlint checker) must be lower case.
+
 The following example commit message demonstrates the use of the
 ``refactor`` type and the ``amu`` scope:
 
@@ -144,7 +147,7 @@
 
 --------------
 
-*Copyright (c) 2021, Arm Limited and Contributors. All rights reserved.*
+*Copyright (c) 2021-2025, Arm Limited and Contributors. All rights reserved.*
 
 .. _Conventional Commits: https://www.conventionalcommits.org/en/v1.0.0
 .. _Gerrit Change-Ids documentation: https://review.trustedfirmware.org/Documentation/user-changeid.html