doc: add Unicode functions to API description

Add include/charset.h to generated HTML documentation

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/doc/api/index.rst b/doc/api/index.rst
index d484c06..2578abd 100644
--- a/doc/api/index.rst
+++ b/doc/api/index.rst
@@ -9,3 +9,4 @@
    efi
    linker_lists
    serial
+   unicode
diff --git a/doc/api/unicode.rst b/doc/api/unicode.rst
new file mode 100644
index 0000000..3fb6745
--- /dev/null
+++ b/doc/api/unicode.rst
@@ -0,0 +1,7 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+Unicode support
+===============
+
+.. kernel-doc:: include/charset.h
+   :internal: