Added gitpod support

.gitpod.yml

@@ -0,0 +1,12 @@
+image:
+  file: Dockerfile
+tasks:
+- command: >
+    mkdir --parents build &&
+    cd build &&
+    cmake .. &&
+    make &&
+    ./tinyraytracer &&
+    pnmtopng out.ppm > out.png &&
+    open out.png &&
+    cd ..

Dockerfile

@@ -0,0 +1,6 @@
+FROM gitpod/workspace-full
+
+USER root
+# add your tools here
+RUN apt-get update && apt-get install -y \
+  netpbm

Readme.md

@@ -17,6 +17,14 @@ cd build
 cmake ..
 make
 ```
+
+You can open the project in Gitpod, a free online dev evironment for GitHub:
+
+[![Open in Gitpod](https://gitpod.io/button/open-in-gitpod.svg)](https://gitpod.io/#https://github.com/ssloy/tinyraytracer)
+
+On open, the editor will compile & run the program as well as open the resulting image in the editor's preview.
+Just change the code in the editor and rerun the script (use the terminal's history) to see updated images.
+
 # Homework assignment
 [homework_assignment branch](https://github.com/ssloy/tinyraytracer/tree/homework_assignment) contains all necessary stuff to easily add environment maps:
 ![](https://raw.githubusercontent.com/ssloy/tinyraytracer/homework_assignment/out-envmap.jpg)