Add comments for ARGBToUV_C and ARGBToUVJ_C

ARGBToUV_C and ARGBToUVJ_C are generated functions with subtle
difference in rounding.  Adding comment to make them easier to find.

TBR=kjellander@chromium.org
BUG=libyuv:634
TEST=untested

Change-Id: I9912d256a1e04c58475d33bdb472c37484f6cab9
Reviewed-on: https://chromium-review.googlesource.com/434980Reviewed-by: Frank Barchard <fbarchard@google.com>
Commit-Queue: Frank Barchard <fbarchard@google.com>

docs/getting_started.md

@@ -212,14 +212,14 @@ Running test with C code:
 
 Install cmake: http://www.cmake.org/
 
-Default debug build:
+### Default debug build:
 
     mkdir out
     cd out
     cmake ..
     cmake --build .
 
-Release build/install
+### Release build/install
 
     mkdir out
     cd out
@@ -227,7 +227,7 @@ Release build/install
     cmake --build . --config Release
     sudo cmake --build . --target install --config Release
 
-Release package
+### Release package
 
     mkdir out
     cd out
@@ -235,6 +235,25 @@ Release package
     make -j4
     make package
 
+## Setup for Arm Cross compile
+
+    See also
+    https://www.ccoderun.ca/programming/2015-12-20_CrossCompiling/index.html#setup
+
+    sudo apt-get install ssh dkms build-essential linux-headers-generic
+    sudo apt-get install kdevelop cmake git subversion
+    sudo apt-get install graphviz doxygen doxygen-gui
+    sudo apt-get install manpages manpages-dev manpages-posix manpages-posix-dev
+    sudo apt-get install libboost-all-dev libboost-dev libssl-dev
+    sudo apt-get install rpm terminator fish
+    sudo apt-get install g++-arm-linux-gnueabihf gcc-arm-linux-gnueabihf
+
+### Build psnr tool
+
+    cd util
+    arm-linux-gnueabihf-g++ psnr_main.cc psnr.cc ssim.cc -o psnr
+    arm-linux-gnueabihf-objdump -d psnr
+
 ## Running Unittests
 
 ### Windows

source/row_common.cc

@@ -314,6 +314,7 @@ static __inline int RGBToV(uint8 r, uint8 g, uint8 b) {
   return (112 * r - 94 * g - 18 * b + 0x8080) >> 8;
 }
 
+// ARGBToY_C and ARGBToUV_C
 #define MAKEROWY(NAME, R, G, B, BPP)                                     \
   void NAME##ToYRow_C(const uint8* src_argb0, uint8* dst_y, int width) { \
     int x;                                                               \
@@ -399,6 +400,7 @@ static __inline int RGBToVJ(uint8 r, uint8 g, uint8 b) {
 
 #define AVGB(a, b) (((a) + (b) + 1) >> 1)
 
+// ARGBToYJ_C and ARGBToUVJ_C
 #define MAKEROWYJ(NAME, R, G, B, BPP)                                     \
   void NAME##ToYJRow_C(const uint8* src_argb0, uint8* dst_y, int width) { \
     int x;                                                                \