docs: add section about installing ts-jest (#12607)

docs/GettingStarted.md

@@ -150,6 +150,10 @@ However, there are some [caveats](https://babeljs.io/docs/en/babel-plugin-transf
 
 [ts-jest](https://github.com/kulshekhar/ts-jest) is a TypeScript preprocessor with source map support for Jest that lets you use Jest to test projects written in TypeScript.
 
+```bash npm2yarn
+npm install --save-dev ts-jest
+```
+
 #### Type definitions
 
 You may also want to install the [`@types/jest`](https://www.npmjs.com/package/@types/jest) module for the version of Jest you're using. This will help provide full typing when writing your tests with TypeScript.

website/versioned_docs/version-25.x/GettingStarted.md

@@ -158,6 +158,10 @@ However, there are some [caveats](https://babeljs.io/docs/en/babel-plugin-transf
 
 [ts-jest](https://github.com/kulshekhar/ts-jest) is a TypeScript preprocessor with source map support for Jest that lets you use Jest to test projects written in TypeScript.
 
+```bash
+yarn add --dev ts-jest
+```
+
 #### Type definitions
 
 You may also want to install the [`@types/jest`](https://www.npmjs.com/package/@types/jest) module for the version of Jest you're using. This will help provide full typing when writing your tests with TypeScript.

website/versioned_docs/version-26.x/GettingStarted.md

@@ -158,6 +158,10 @@ However, there are some [caveats](https://babeljs.io/docs/en/babel-plugin-transf
 
 [ts-jest](https://github.com/kulshekhar/ts-jest) is a TypeScript preprocessor with source map support for Jest that lets you use Jest to test projects written in TypeScript.
 
+```bash
+yarn add --dev ts-jest
+```
+
 ### Using TypeScript: type definitions
 
 You may also want to install the [`@types/jest`](https://www.npmjs.com/package/@types/jest) module for the version of Jest you're using. This will help provide full typing when writing your tests with TypeScript.

website/versioned_docs/version-27.0/GettingStarted.md

@@ -158,6 +158,10 @@ However, there are some [caveats](https://babeljs.io/docs/en/babel-plugin-transf
 
 [ts-jest](https://github.com/kulshekhar/ts-jest) is a TypeScript preprocessor with source map support for Jest that lets you use Jest to test projects written in TypeScript.
 
+```bash
+yarn add --dev ts-jest
+```
+
 #### Type definitions
 
 You may also want to install the [`@types/jest`](https://www.npmjs.com/package/@types/jest) module for the version of Jest you're using. This will help provide full typing when writing your tests with TypeScript.

website/versioned_docs/version-27.1/GettingStarted.md

@@ -158,6 +158,10 @@ However, there are some [caveats](https://babeljs.io/docs/en/babel-plugin-transf
 
 [ts-jest](https://github.com/kulshekhar/ts-jest) is a TypeScript preprocessor with source map support for Jest that lets you use Jest to test projects written in TypeScript.
 
+```bash
+yarn add --dev ts-jest
+```
+
 #### Type definitions
 
 You may also want to install the [`@types/jest`](https://www.npmjs.com/package/@types/jest) module for the version of Jest you're using. This will help provide full typing when writing your tests with TypeScript.

website/versioned_docs/version-27.2/GettingStarted.md

@@ -158,6 +158,10 @@ However, there are some [caveats](https://babeljs.io/docs/en/babel-plugin-transf
 
 [ts-jest](https://github.com/kulshekhar/ts-jest) is a TypeScript preprocessor with source map support for Jest that lets you use Jest to test projects written in TypeScript.
 
+```bash
+yarn add --dev ts-jest
+```
+
 #### Type definitions
 
 You may also want to install the [`@types/jest`](https://www.npmjs.com/package/@types/jest) module for the version of Jest you're using. This will help provide full typing when writing your tests with TypeScript.

website/versioned_docs/version-27.4/GettingStarted.md

@@ -158,6 +158,10 @@ However, there are some [caveats](https://babeljs.io/docs/en/babel-plugin-transf
 
 [ts-jest](https://github.com/kulshekhar/ts-jest) is a TypeScript preprocessor with source map support for Jest that lets you use Jest to test projects written in TypeScript.
 
+```bash
+yarn add --dev ts-jest
+```
+
 ### Using TypeScript: type definitions
 
 You may also want to install the [`@types/jest`](https://www.npmjs.com/package/@types/jest) module for the version of Jest you're using. This will help provide full typing when writing your tests with TypeScript.

website/versioned_docs/version-27.5/GettingStarted.md

@@ -158,6 +158,10 @@ However, there are some [caveats](https://babeljs.io/docs/en/babel-plugin-transf
 
 [ts-jest](https://github.com/kulshekhar/ts-jest) is a TypeScript preprocessor with source map support for Jest that lets you use Jest to test projects written in TypeScript.
 
+```bash
+yarn add --dev ts-jest
+```
+
 You may also want to install the [`@types/jest`](https://www.npmjs.com/package/@types/jest) module for the version of Jest you're using. This will help provide full typing when writing your tests with TypeScript.
 
 > For `@types/*` modules it's recommended to try to match the version of the associated module. For example, if you are using `26.4.0` of `jest` then using `26.4.x` of `@types/jest` is ideal. In general, try to match the major (`26`) and minor (`4`) version as closely as possible.