Add default permissions as read-only (#75)

* Add default permissions as read-only

Setting this will increase the openssf score.

* Fix build badge

.github/workflows/ci.yml

@@ -7,6 +7,9 @@ on:
       - 'v*.[0-9]'
   pull_request:
 
+permissions:
+  contents: read
+
 jobs:
   tests:
     name: Run tests

README.md

@@ -1,5 +1,5 @@
 # Elixir XDR
-![Build Badge](https://img.shields.io/github/actions/workflow/status/kommitters/elixir_xdr/CI.yml?branch=main&style=for-the-badge)
+![Build Badge](https://img.shields.io/github/actions/workflow/status/kommitters/elixir_xdr/ci.yml?branch=main&style=for-the-badge)
 [![Coverage Status](https://img.shields.io/coveralls/github/kommitters/elixir_xdr?style=for-the-badge)](https://coveralls.io/github/kommitters/elixir_xdr)
 [![Version Badge](https://img.shields.io/hexpm/v/elixir_xdr?style=for-the-badge)](https://hexdocs.pm/elixir_xdr)
 ![Downloads Badge](https://img.shields.io/hexpm/dt/elixir_xdr?style=for-the-badge)