add small documentation to readme

oss-internship-2020/libpng/README.md

@@ -0,0 +1,36 @@
+# sandboxed LibPNG
+Copyright 2020 Google LLC.
+
+## Start use
+You should make sure the libtiff submodule is cloned.
+
+`git clone --recursive https://github.com/google/sandboxed-api`
+
+## Usage
+
+#### Build:
+```
+mkdir -p build && cd build && \
+	cmake .. -DSAPI_ROOT=/path/to/sapi_root
+make -j8
+```
+
+#### Example:
+You should add `-DLIBPNG_SAPI_ENABLE_EXAMPLES=ON` to use the example.\
+run PNG to PNG: `./examples/pngtopng /absolute/path/to/input/image.png /absolute/path/to/output/image.png`\
+run RGB to BGR: `./examples/rgbtobgr /absolute/path/to/input/image.png /absolute/path/to/output/image.png`
+
+Input and output examples can be found in images directory.
+
+PNG to PNG: \
+input: `/abs/path/to/project/images/pngtest.png`\
+output:` /abs/path/to/project/images/pngtopng_pngtest.png`
+
+RGB to BGR: \
+input: `/abs/path/to/project/images/red_ball.png`\
+output:` /abs/path/to/project/images/rgbtobgr_red_ball.png`
+
+
+#### Tests:
+You should add `-DLIBPNG_SAPI_ENABLE_TESTS=ON` to use tests.\
+run: `./tests/tests`

oss-internship-2020/libpng/tests/libpng.h

@@ -13,7 +13,7 @@
 // limitations under the License.
 
 // Defines from libpng library. The problem is that the build throws the error
-// "Duplicate functions" if #include <png.h> was added.
+// "Duplicate functions" if #include <png.h> is added.
 
 #define PNG_FORMAT_FLAG_ALPHA 0x01U
 #define PNG_FORMAT_FLAG_COLOR 0x02U