docs: add PULL_REQUEST_TESTS.md (#171)

Author: Vasil Chimev

Diff for: PULL_REQUEST_TESTS.md

@@ -0,0 +1,10 @@
+This document describes comment messages available to execute tests on pull request.
+
+|Comment                 |Commit Status Context|Description|
+|:----------------------:|:-------------------:|:---------:|
+|`run ci`                |                     |Run all below.|
+|`js`|ci/jenkins/webpack-js|Pack the *nativescript-dev-webpack* plugin and bundle the [template-hello-world](https://github.com/NativeScript/template-hello-world) template app.      |
+|`ts`|ci/jenkins/webpack-ts|Pack the *nativescript-dev-webpack* plugin and bundle the [template-hello-world-ts](https://github.com/NativeScript/template-hello-world-ts) template app.|
+|`ng`|ci/jenkins/webpack-ng|Pack the *nativescript-dev-webpack* plugin and bundle the [template-hello-world-ng](https://github.com/NativeScript/template-hello-world-ng) template app.|
+|`groceries`|ci/jenkins/webpack-groceries|Pack the *nativescript-dev-webpack* plugin and bundle the [Groceries](https://github.com/NativeScript/sample-Groceries) app.                |
+|`sdk`|ci/jenkins/webpack-sdk|Pack the *nativescript-dev-webpack* plugin and bundle the [SDK](https://github.com/NativeScript/nativescript-sdk-examples-ng) app.                      |