Add comments about the -shared flag.

Must build this linker as a shared object.
A statically linked module does not load during init.

BUG: 18008984

Change-Id: I5f0411129024edcb9381c473ea4e741a075e9184
diff --git a/linker/Android.mk b/linker/Android.mk
index e1302db..989b0d2 100644
--- a/linker/Android.mk
+++ b/linker/Android.mk
@@ -19,6 +19,9 @@
 LOCAL_SRC_FILES_mips    := arch/mips/begin.S linker_mips.cpp
 LOCAL_SRC_FILES_mips64  := arch/mips64/begin.S linker_mips.cpp
 
+# -shared is used to overwrite the -Bstatic and -static
+# flags triggered by LOCAL_FORCE_STATIC_EXECUTABLE.
+# This dynamic linker is actually a shared object linked with static libraries.
 LOCAL_LDFLAGS := \
     -shared \
     -Wl,-Bsymbolic \