Project setup (#1)

This PR contains the work done to setup the project:
* Added the `hummingbird` and the `swift-dock-plugin` package dependencies to the `Package` file;
* Added the `Makefile` file with relevant tasks plus its related `.env` file;
* Added the `CONTRIBUTORS` and `LICENSE` files;
* Added the `README` file;
* Updated the `.gitignore` file.

Reviewed-on: rock-n-code/hummingbird-docc-middleware#1
Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>
Co-committed-by: Javier Cicchelli <javier@rock-n-code.com>

.env

@@ -0,0 +1,22 @@
+# ===----------------------------------------------------------------------===
+# 
+# This source file is part of the Hummingbird DocC Middleware open source project
+# 
+# Copyright (c) 2025 Röck+Cöde VoF. and the Hummingbird DocC Middleware project authors
+# Licensed under the EUPL 1.2 or later.
+# 
+# See LICENSE for license information
+# See CONTRIBUTORS for the list of Hummingbird DocC Middleware project authors
+# 
+# ===----------------------------------------------------------------------===
+
+# --- DOCUMENTATION ---
+
+DOCC_GITHUB_OUTPUT=./docs
+DOCC_GITHUB_BASE_PATH=hummingbird-docc-middleware
+DOCC_PREVIEW_URL=http://localhost:8080/documentation/doccmiddleware
+DOCC_XCODE_OUTPUT=./${SPM_LIBRARY_TARGET}.doccarchive
+
+# -- SWIFT PACKAGE MANAGER ---
+
+SPM_LIBRARY_TARGET=DocCMiddleware