Ensure plugin is included in sdist build

Author: rlaboiss

pyproject.toml

@@ -40,6 +40,8 @@ Funding = "https://donate.getpelican.com/"
 [project.optional-dependencies]
 markdown = ["markdown>=3.4"]
 
+[tool.pdm]
+
 [tool.pdm.dev-dependencies]
 lint = [
     "black>=23.10.1",
@@ -53,6 +55,14 @@ test = [
     "pytest-sugar>=0.9.7",
 ]
 
+[tool.pdm.build]
+source-includes = [
+    "CHANGELOG.md",
+    "CONTRIBUTING.md",
+]
+includes = ["pelican/"]
+excludes = ["tasks.py"]
+
 [tool.autopub]
 project-name = "Markdown Include"
 git-username = "botpub"