Merge pull request #10063 from davidhorstmann-arm/update-3.0-migration-guide

Update the 3.0 migration guide and fix broken README link
diff --git a/include/mbedtls/net_sockets.h b/include/mbedtls/net_sockets.h
index 85c1197..8e69bc0 100644
--- a/include/mbedtls/net_sockets.h
+++ b/include/mbedtls/net_sockets.h
@@ -229,7 +229,7 @@
 
 /**
  * \brief          Write at most 'len' characters. If no error occurs,
- *                 the actual amount read is returned.
+ *                 the actual amount written is returned.
  *
  * \param ctx      Socket
  * \param buf      The buffer to read from