Added how to use

Signed-off-by: Trial97 <[email protected]>

Author: Trial97

README.md

@@ -1,3 +1,10 @@
 # changelog-generator
 
-tbd
+## How to use
+
+- run `nix develop`
+- create a read-only Github Token
+- set GITHUB_TOKEN environment variable to that value
+- run `python -m changelog_generator {owner}/{repo} {milestone}`
+
+e.g `python -m changelog_generator Prismlauncher/PrismLauncher 8.3`