Update CONTRIBUTING.md

Author: nicolaskruchten

CONTRIBUTING.md

@@ -1,8 +1,16 @@
 # Contributing to Plotly.js
 
-### How do changes get made to Plotly.js?
+Thanks for your interesting in contributing to Plotly.js!
 
-The basic architecture of Plotly.js is to accept [JSON](https://json.org/) representation of figures that adhere to the [figure schema](https://plotly.com/javascript/reference/index/) and draw graphical representations of these figures. A **new feature** is composed of additions to the schema - adding new attributes, adding entire new trace types, or just adding new values to existing attributes - along with the associated drawing code. This project has a strong commitment to backwards-compatibility,  so changing the graphical output for existing schema attributes and values, or changing the default value of an attribute, is generally only done as a mostly-backwards-compatible **bug fix**, for cases when the current graphical output is incorrect, nonsensical or otherwise very problematic.  Non-schema-related features and bug fixes are possible as well, usually around performance, security, bundling, function signatures etc, and generally follow the same principles.
+## Plotly.js vs Plotly.py and Plotly.R
+
+[Plotly.js](https://plotly.com/javascript) is a standalone Javascript data visualization library, and it also powers the Python and R modules named `plotly` in those respective ecosystems (referred to as [Plotly.py](https://plotly.com/python) and [Plotly.R](http://plotly.com/r), respectively, for clarity). There also exist Plotly.js-powered libraries for other languages such as Julia, Scala, Rust, .NET and even C++!
+
+The basic architecture of Plotly.js is to accept [JSON](https://json.org/) representation of figures that adhere to the [figure schema](https://plotly.com/javascript/reference/index/) and draw interactive graphical representations of these figures in a browser. Libraries in other languages like Python and R provide idiomatic interfaces for users of those languages to create and manipulate these JSON structures, and arrange for them to be rendered in a browser context by Plotly.js. This means that in many cases, when a Python or R user wishes to add a feature to the library they know as `plotly`, the relevant changes must be implemented in Plotly.js, in this repo.
+
+## How do changes get made to Plotly.js?
+
+ A **new feature** is composed of additions to the schema - adding new attributes, adding entire new trace types, or just adding new values to existing attributes - along with the associated drawing code. This project has a strong commitment to backwards-compatibility,  so changing the graphical output for existing schema attributes and values, or changing the default value of an attribute, is generally only done as a mostly-backwards-compatible **bug fix**, for cases when the current graphical output is incorrect, nonsensical or otherwise very problematic.  Non-schema-related features and bug fixes are possible as well, usually around performance, security, bundling, function signatures etc, and generally follow the same principles.
 
 The basic process for adding new features or fixing bugs is as follows: