Update user guide further to linker scripts changes

This patch updates the user guide section about the memory layout.
  - Explain the verifications that the linker scripts does on the
    global memory layout.
  - Refer to the new linker symbols.
  - Describe the linker symbols exported to the trusted firmware code.

Change-Id: I033ab2b867e8b9776deb4185b9986bcb8218f286
diff --git a/docs/change-log.md b/docs/change-log.md
index ca3cb7f..963f578 100644
--- a/docs/change-log.md
+++ b/docs/change-log.md
@@ -26,6 +26,20 @@
 
 *   Build products are now created in a separate build directory tree.
 
+*   Analyze at link-time whether bootloader images will fit in memory and won't
+    overlap each other at run time. If it is not the case then image linking
+    will now fail.
+
+*   Reduce the size of the bootloader images by cutting some sections out of
+    their disk images and allocating them at load time, whenever possible.
+
+*   Properly initialise the C runtime environment. C code can now safely assume
+    that global variables are initialised to 0 and that initialised data holds
+    the correct value.
+
+*   General changes on the memory layout: some sections have been moved, some of
+    them have been merged together, and some alignment constraints on sections
+    have changed.
 
 ARM Trusted Firmware - version 0.2
 ==================================