Update README.md

Author: mlejva

README.md

@@ -36,7 +36,7 @@ pip install e2b-code-interpreter
 ### 2. Get your E2B API key
 1. Sign up to E2B [here](https://e2b.dev).
 2. Get your API key [here](https://e2b.dev/dashboard?tab=keys).
-3. Set environment variable with your API key
+3. Set environment variable with your API key.
 ```
 E2B_API_KEY=e2b_***
 ```