Add contributing guideline and remove unneeded parts

.github/SAMPLE_GUIDELINE.md

@@ -0,0 +1,11 @@
+# Sample Guideline
+
+Each sample should have the following components and structure, so that users could have a smooth experience when playing with the samples.
+
+## README
+
+- Each README should start with a short sentence / paragraph that describes what the extensions is and what it is meant to illustrate.
+- If the sample has a corresponding guide, it should link to the guide.
+- If the illustrated functionality is visual, a gif/image should follow the explanation.
+- A `Running the sample` section should describe the actions to run the sample.
+  - Mostly, it should be: Open this sample in VS Code -> `npm install && npm compile` -> Run `Launch Sample` target.