ci(workflow): add documentation workflow (#170)

Author: Sven

.github/workflows/docs.yml

@@ -0,0 +1,39 @@
+name: Continuous Integration - Docs
+
+on:
+  push:
+    branches:
+      - master
+    paths:
+      - "**.rs"
+      - "Cargo.toml"
+      - "Cargo.lock"
+
+jobs:
+  docs:
+    name: Generate crate documentation
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout sources
+        uses: actions/checkout@v2
+
+      - name: Install Rust toolchain
+        uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: nightly
+          override: true
+
+      - name: Generate documentation
+        uses: actions-rs/cargo@v1
+        env:
+          RUSTDOCFLAGS: "--enable-index-page -Zunstable-options"
+        with:
+          command: doc
+          args: --workspace --no-deps
+
+      - name: Deploy documentation
+        uses: peaceiris/actions-gh-pages@v3
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          publish_dir: ./target/doc

README.md

@@ -1,4 +1,9 @@
-env_logger [![Build Status](https://travis-ci.org/sebasmagri/env_logger.svg?branch=master)](https://travis-ci.org/sebasmagri/env_logger) [![Maintenance](https://img.shields.io/badge/maintenance-actively%20maintained-brightgreen.svg)](https://github.com/sebasmagri/env_logger) [![crates.io](https://img.shields.io/crates/v/env_logger.svg)](https://crates.io/crates/env_logger) [![Documentation](https://img.shields.io/badge/docs-current-blue.svg)](https://docs.rs/env_logger)
+# env_logger 
+[![Build Status](https://travis-ci.org/sebasmagri/env_logger.svg?branch=master)](https://travis-ci.org/sebasmagri/env_logger)
+[![Maintenance](https://img.shields.io/badge/maintenance-actively%20maintained-brightgreen.svg)](https://github.com/sebasmagri/env_logger)
+[![crates.io](https://img.shields.io/crates/v/env_logger.svg)](https://crates.io/crates/env_logger)
+[![Documentation](https://docs.rs/env_logger/badge.svg)](https://docs.rs/env_logger)
+[![Documentation](https://img.shields.io/badge/docs-master-blue.svg)](https://env-logger-rs.github.io/env_logger)
 ==========
 
 Implements a logger that can be configured via environment variables.