Experimental: document that cmake + c api example now works in Ubuntu.

experimental/c-api-example/c.md

 Skia's Stable C API
 ===================
 
 <div style="text-align:center">
 <strong>EXPERIMENTAL EXPERIMENTAL EXPERIMENTAL EXPERIMENTAL<br>
 DO NOT USE &mdash; FOR INTERNAL TESTING ONLY</strong>
 </div>
 
 Several issues hinder the development of a stable ABI (application
 binary interface) for Skia:
@@ skipping 85 matching lines @@
         sk_surface_t* surface = make_surface(640, 480);
         sk_canvas_t* canvas = sk_surface_get_canvas(surface);
         draw(canvas);
         emit_png("skia-c-example.png", surface);
         sk_surface_unref(surface);
         return 0;
     }
 
 <a href="https://fiddle.skia.org/c/6c6c01438d9c3d80e9c22e606359432e"><img src="https://fiddle.skia.org/i/6c6c01438d9c3d80e9c22e606359432e_raster.png" alt=""></a>
 
+<!--
+
 Gyp+Linux example
 -----------------
 
 The following proof-of-concept workflow currently works on Ubuntu 14.04:
 
 1.  Aquire Skia and install dependencies (you may have already done this):
 
     <!--?prettify lang=sh?-->
 
         git clone 'https://chromium.googlesource.com/chromium/tools/depot_tools.git'
@@ skipping 12 matching lines @@
 3.  Compile, link, and run the example program:
 
     <!--?prettify lang=sh?-->
 
         cd [Wherever you want the example]
         cp "$SKIA_DIR/experimental/c-api-example/skia-c-example.c" .
         cc -c -I "$SKIA_DIR/include/c" skia-c-example.c -o skia-c-example.o
         cc skia-c-example.o -L "$SKIA_DIR/out/Release/lib" -lskia -o skia-c-example
         LD_LIBRARY_PATH="$SKIA_DIR/out/Release/lib" ./skia-c-example
         xdg-open skia-c-example.png
+-->
 
-Cmake+MacOS example
--------------------
+Cmake example
+-------------
 
-The following proof-of-concept workflow currently works on MacOS
+The following proof-of-concept workflow currently works on MacOS and Ubuntu
 
-1.  Aquire Skia and install dependencies (you may have already done this):
+1.  Aquire Skia (you may have already done this):
 
     <!--?prettify lang=sh?-->
 
         cd [Wherever you want skia src code]
         git clone 'https://skia.googlesource.com/skia'
         SKIA_DIR="$PWD/skia"
 
-2.  Compile Skia as a shared library:
+2.  Compile Skia (outside of source) as a shared library:
 
     <!--?prettify lang=sh?-->
 
         cd [Wherever you want skia build files]
         mkdir build_skia
         cd build_skia
         SKIA_BUILD="$PWD"
         cmake "$SKIA_DIR/cmake" -G Ninja && ninja
 
 3.  Compile, link, and run the example program:
 
     <!--?prettify lang=sh?-->
 
         cd [Wherever you want the example]
+        mkdir skia_c_example
+        cd skia_c_example
         cp "$SKIA_DIR/experimental/c-api-example/skia-c-example.c" .
         cc -c -I "$SKIA_DIR/include/c" skia-c-example.c -o skia-c-example.o
         c++ skia-c-example.o \
             "$SKIA_BUILD"/libskia.* -Wl,-rpath -Wl,"$SKIA_BUILD" \
             -o skia-c-example
         ./skia-c-example
-        open skia-c-example.png
+        [ $(uname) = Darwin ] && open skia-c-example.png
+        [ $(uname) = Linux ] && xdg-open skia-c-example.png