add local testing info

Author: rezkiy37

README.md

@@ -12,6 +12,27 @@ Awesome PDF viewer, that combines the best of others into one tool.
 - Easy customized.
 - Support by Expensify.
 
+# Local testing
+
+Actually, for testing changes locally, we need to connect `example` to the code from `src` directory (_**NPM** by default_).
+
+Update a few fields in `example` directory:
+1. `package.json`:
+```diff
+-"react-fast-pdf": "^1.*"
++"react-fast-pdf": "../src"
+```
+
+2. `tsconfig.json`:
+```diff
+-"rootDir": "./src"
++"rootDir": "../"
+```
+
+3. Run `npm i` in the directory. It should update `package-lock.json`.
+
+The final result has to look like in this [commit](https://github.com/Expensify/react-fast-pdf/pull/9/commits/29334948a936def7a1ba967aa632f6f5e951a3cb).
+
 # Deploying
 
 This repo automatically publishes to NPM when PRs are merged to main.