readme updated

Author: smriti1313

Caesar-Cipher/README.md

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+## Caesar-cipher:
+Caesar's cipher, the shift cipher, is one of the simplest and most widely known encryption techniques. It is a type of substitution cipher in which each letter in the plaintext is replaced by a letter some fixed number of positions down the alphabet.
+
+
+### How to run this:
+
+- Simply copy-paste the code in your editor and run it using:
+
+```python
+python3 caesar_cipher.py
+```
+
+### Output:
+
+![](output.png)
+
+> Learn more about this [here.](https://www.youtube.com/watch?v=fR8rVR72a6o)