Update docs

Author: nekeal

CHANGELOG.md

@@ -6,6 +6,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 ## Unreleased
 ### Added
 - Extend cli with possibility to specify directories for: templates, challenges solutions, and data
+- Extend cli and `BaseChallenge` interface with possibility to specify custom input file
 
 ### Fixed
 - Fixed typing in cli module

README.md

@@ -66,6 +66,15 @@ Day 0 - Part 1: 1
 Day 0 - Part 2: 10
 ```
 
+Alternatively you can also specify the path to the input file instead of using the default one.
+
+```sh
+$ aoc run 0 -f custom_input.txt
+Using data from custom_input.txt                                                                                                        hello, nekeal ⭐
+Day 0 - Part 1: 1
+Using data from custom_input.txt
+Day 0 - Part 2: 33
+```
 ### Verifying solution
 
 You can verify your solution by running [pytest](https://github.com/pytest-dev/pytest) tests.