Replace reference to master

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/BRANCHES.md b/BRANCHES.md
index 0ed2099..bcceda8 100644
--- a/BRANCHES.md
+++ b/BRANCHES.md
@@ -2,7 +2,7 @@
 
 At any point in time, we have a number of maintained branches, currently consisting of:
 
-- The [`master`](https://github.com/Mbed-TLS/mbedtls/tree/master) branch:
+- The [`main`](https://github.com/Mbed-TLS/mbedtls/tree/main) branch:
   this always contains the latest release, including all publicly available
   security fixes.
 - The [`development`](https://github.com/Mbed-TLS/mbedtls/tree/development) branch:
@@ -19,7 +19,7 @@
 These branches will not receive any changes or updates.
 
 We use [Semantic Versioning](https://semver.org/). In particular, we maintain
-API compatibility in the `master` branch across minor version changes (e.g.
+API compatibility in the `main` branch across minor version changes (e.g.
 the API of 3.(x+1) is backward compatible with 3.x). We only break API
 compatibility on major version changes (e.g. from 3.x to 4.0). We also maintain
 ABI compatibility within LTS branches; see the next section for details.
@@ -103,7 +103,7 @@
 
 The following branches are currently maintained:
 
-- [master](https://github.com/Mbed-TLS/mbedtls/tree/master)
+- [main](https://github.com/Mbed-TLS/mbedtls/tree/main)
 - [`development`](https://github.com/Mbed-TLS/mbedtls/)
 - [`mbedtls-3.6`](https://github.com/Mbed-TLS/mbedtls/tree/mbedtls-3.6)
  maintained until March 2027, see