docs: add basic intro page for C# (#6110)

docs/src/intro-csharp.md

@@ -0,0 +1,59 @@
+---
+id: intro
+title: "Getting Started"
+---
+
+<!-- TOC -->
+- [Release notes](./release-notes.md)
+
+## Installation
+
+Install PlaywrightSharp package from NuGet in Visual Studio or from the CLI in your project root directory:
+
+```sh
+dotnet add package PlaywrightSharp
+```
+
+## Usage
+
+```csharp
+using var playwright = await Playwright.CreateAsync();
+await using var browser = await playwright.Chromium.LaunchAsync();
+var page = await browser.NewPageAsync();
+await page.GoToAsync("http://www.bing.com");
+await page.ScreenshotAsync(path: outputFile);
+```
+
+## First script
+
+In our first script, we will navigate to `whatsmyuseragent.org` and take a screenshot in WebKit.
+
+```csharp
+// FIXME:
+```
+
+By default, Playwright runs the browsers in headless mode. To see the browser UI, pass the `headless=False` flag while launching the browser. You can also use [`option: slowMo`] to slow down execution. Learn more in the debugging tools [section](./debug.md).
+
+```csharp
+// FIXME:
+```
+
+## Record scripts
+
+Command Line Interface [CLI](./cli.md) can be used to record user interactions and generate C# code.
+
+```sh
+# FIXME:
+```
+
+## System requirements
+
+The browser binaries for Chromium, Firefox and WebKit work across the 3 platforms (Windows, macOS, Linux):
+
+* **Windows**: Works with Windows and Windows Subsystem for Linux (WSL).
+* **macOS**: Requires 10.14 or above.
+* **Linux**: Depending on your Linux distribution, you might need to install additional
+  dependencies to run the browsers.
+  * Firefox requires Ubuntu 18.04+
+  * For Ubuntu 20.04, the additional dependencies are defined in [our Docker image](https://github.com/microsoft/playwright/blob/master/utils/docker/Dockerfile.focal),
+    which is based on Ubuntu.

docs/src/intro-java.md

@@ -133,5 +133,5 @@ Firefox and WebKit work across the 3 platforms (Windows, macOS, Linux):
 * **Linux**: Depending on your Linux distribution, you might need to install additional
   dependencies to run the browsers.
   * Firefox requires Ubuntu 18.04+
-  * For Ubuntu 18.04, the additional dependencies are defined in [our Docker image](https://github.com/microsoft/playwright/blob/master/utils/docker/Dockerfile.bionic),
+  * For Ubuntu 20.04, the additional dependencies are defined in [our Docker image](https://github.com/microsoft/playwright/blob/master/utils/docker/Dockerfile.focal),
     which is based on Ubuntu.

docs/src/intro-js.md

@@ -105,5 +105,5 @@ Firefox and WebKit work across the 3 platforms (Windows, macOS, Linux):
 * **Linux**: Depending on your Linux distribution, you might need to install additional
   dependencies to run the browsers.
   * Firefox requires Ubuntu 18.04+
-  * For Ubuntu 18.04, the additional dependencies are defined in [our Docker image](https://github.com/microsoft/playwright/blob/master/utils/docker/Dockerfile.bionic),
+  * For Ubuntu 20.04, the additional dependencies are defined in [our Docker image](https://github.com/microsoft/playwright/blob/master/utils/docker/Dockerfile.focal),
     which is based on Ubuntu.

docs/src/intro-python.md

@@ -88,5 +88,5 @@ Firefox and WebKit work across the 3 platforms (Windows, macOS, Linux):
 * **Linux**: Depending on your Linux distribution, you might need to install additional
   dependencies to run the browsers.
   * Firefox requires Ubuntu 18.04+
-  * For Ubuntu 18.04, the additional dependencies are defined in [our Docker image](https://github.com/microsoft/playwright/blob/master/utils/docker/Dockerfile.bionic),
+  * For Ubuntu 20.04, the additional dependencies are defined in [our Docker image](https://github.com/microsoft/playwright/blob/master/utils/docker/Dockerfile.focal),
     which is based on Ubuntu.