Docs: return .align 4 into C startup code

Signed-off-by: Pavel Pisa <[email protected]>

Author: ppisa

docs/user/reference/external_toolchains.md

@@ -85,6 +85,8 @@ _exit:
 
 .bss
 
+.align 4
+
 /* the area which can be used for a heap from the bootom
  * and stack from the top
  */