docs: improved Flow documentation

docusaurus/docs/adding-flow.md

@@ -17,6 +17,8 @@ To add Flow to a Create React App project, follow these steps:
 Now you can run `npm run flow` (or `yarn flow`) to check the files for type errors.  
 You can optionally enable an extension for your IDE, such as [Flow Language Support](https://github.com/flowtype/flow-for-vscode) for Visual Studio Code, or leverage the Language Server Protocol standard (e.g. [vim LSP](https://github.com/prabirshrestha/vim-lsp/wiki/Servers-Flow)) to get hints while you type.
 
+## Absolute Imports
+
 If you'd like to use [absolute imports](/docs/importing-a-component#absolute-imports) with Flow,
 make sure to add the following line to your `.flowconfig` to make Flow aware of it:
 
@@ -25,4 +27,33 @@ make sure to add the following line to your `.flowconfig` to make Flow aware of
 + module.name_mapper='^\([^\.].*\)$' -> '<PROJECT_ROOT>/src/\1'
 ```
 
+## Using the new JSX transform
+
+To enable Flow to use the new JSX transform, you need to enable it in your `.flowconfig` file:
+
+```diff
+  [options]
++ react.runtime=automatic
+```
+
+## Working with 3rd party type definitions
+
+npm packages can come with built-in Flow type definitions, unfortunately, sometimes those type definitions are not fully-compatible with
+the Flow version your project uses, or contain some errors.
+
+Normally, Flow would throw errors, as if you had control over these 3rd party type definitions, but unfortunately you can't directly fix them.
+
+Flow supports a way to define some type definitions as "declarations", this will tell Flow to **use** the type definitions, but to ignore any
+errors that happen inside them.
+
+You can configure your `.flowconfig` with the following lines:
+
+```diff
++ [declarations]
++ <PROJECT_ROOT>/node_modules
+```
+
+Note, `declarations` and `ignore` are not the same thing, the latter will completely ignore the node modules type definitions, while the former
+will use them, but suppress the errors targeting the type definitions.
+
 To learn more about Flow, check out [its documentation](https://flow.org/).