fix project_slug error.

replace ml_pipeline with project_name or module_name from config

{{cookiecutter.project_name}}/docs/.gitignore

@@ -0,0 +1 @@
+book

{{cookiecutter.project_name}}/docs/book.toml

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+[book]
+authors = ["publicmatt"]
+language = "en"
+multilingual = false
+src = "src"
+title = "{{cookiecutter.project_name}}"

{{cookiecutter.project_name}}/docs/src/SUMMARY.md

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+# Summary
+
+- [Overview](./index.md)
+- [Chapter 1](./chapter_1.md)
+

{{cookiecutter.project_name}}/docs/src/chapter_1.md

@@ -0,0 +1 @@
+# Chapter 1

{{cookiecutter.project_name}}/docs/src/index.md

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+# Overview