Bump version to 5.0.0-alpha1 (#29925)

Also add v4.5.0 in versions and keep README.md pointing to v4.5.0 so that there are no broken stuff.

site/content/docs/5.0/getting-started/best-practices.md

@@ -0,0 +1,20 @@
+---
+layout: docs
+title: Best practices
+description: Learn about some of the best practices we've gathered from years of working on and using Bootstrap.
+group: getting-started
+---
+
+We've designed and developed Bootstrap to work in a number of environments. Here are some of the best practices we've gathered from years of working on and using it ourselves.
+
+{{< callout info >}}
+**Heads up!** This copy is a work in progress.
+{{< /callout >}}
+
+### General outline
+
+- Working with CSS
+- Working with Sass files
+- Building new CSS components
+- Working with flexbox
+- Ask in [Slack](https://bootstrap-slack.herokuapp.com/)