Mention transparency mode.

README.md

@@ -3,7 +3,7 @@
 Preview any size image in a terminal window.
 
 
-![Sample use](images/sampledesktop.png "Sample use.")
+![imcat tiger](images/imcat_tiger.png "imcat tiger")
 
 # Platform
 
@@ -22,6 +22,18 @@ It automatically resizes to the width of your terminal, using proper sampling ke
 
 imcat also works on the latest version of Windows 10.
 
+## Usage
+
+```
+$ imcat file1 [file2 .. fileN]
+```
+
+If you want to blend the image with the terminal background, then you need to specify the background color of your terminal. For instance:
+
+```
+$ export IMCATBG="#dad9cc"
+```
+
 ## Todo
 
 * Handle alpha-transparency. Requires reading the terminal background colour, somehow. Tricky.
@@ -48,7 +60,11 @@ On Windows, you need clang.exe from Visual Studio 2017 to build the imcat.exe bi
 
 [stb_image.h](http://nothings.org/stb_image.h) is by Sean Barrett et al.
 
-## Acknoledgements
+## Acknowledgements
 
 A shout out to [Frogtoss](http://github.com/mlabbe) for the idea and help. Thanks!
 
+## Gallery
+
+![Sample use](images/sampledesktop.png "Sample use.")
+