Add a section heading for LTS branches

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/BRANCHES.md b/BRANCHES.md
index d9de695..a758d08 100644
--- a/BRANCHES.md
+++ b/BRANCHES.md
@@ -28,7 +28,7 @@
 modification with any later release x.y'.z' with the same major version
 number, and your code will still build, be secure, and work.
 
-Note that new releases of Mbed TLS may extend the API. Here are some example of changes that are common in minor releases of Mbed TLS, and are not considered API compatibility breaks:
+Note that new releases of Mbed TLS may extend the API. Here are some examples of changes that are common in minor releases of Mbed TLS, and are not considered API compatibility breaks:
 
 * Adding or reordering fields in a structure or union.
 * Removing a field from a structure, unless the field is documented as public.
@@ -43,6 +43,8 @@
 comes in conflict with backwards compatibility, we will put security first,
 but always attempt to provide a compatibility option.
 
+## Long-time support branches
+
 For the LTS branches, additionally we try very hard to also maintain ABI
 compatibility (same definition as API except with re-linking instead of
 re-compiling) and to avoid any increase in code size or RAM usage, or in the