Add copy button in README.md (#965)

Co-authored-by: Pieter Marsman <[email protected]>

README.md

@@ -41,25 +41,26 @@ How to use
 
 * Install Python 3.8 or newer.
 * Install pdfminer.six.
-
-  `pip install pdfminer.six`
+  ```bash
+  pip install pdfminer.six
 
 * (Optionally) install extra dependencies for extracting images.
 
-  `pip install 'pdfminer.six[image]'`
+  ```bash
+  pip install 'pdfminer.six[image]'
 
 * Use the command-line interface to extract text from pdf.
 
-  `pdf2txt.py example.pdf`
+  ```bash
+  pdf2txt.py example.pdf
 
 * Or use it with Python. 
+  ```python
+  from pdfminer.high_level import extract_text
 
-```python
-from pdfminer.high_level import extract_text
-
-text = extract_text("example.pdf")
-print(text)
-```
+  text = extract_text("example.pdf")
+  print(text)
+  ```
 
 Contributing
 ------------