Documentation: Extend "Developer documentation" (rust-lang#988)

* Documentation: Extend "Developer documentation"

* Update docs/src/dev-documentation.md

Co-authored-by: Zyad Hassan <[email protected]>

Author: 2 people

docs/src/dev-documentation.md

@@ -6,3 +6,14 @@ The easiest way to contribute is to [report any
 issue](https://github.com/model-checking/kani/issues/new/choose) you encounter
 while using the tool. If you want to contribute to its development,
 we recommend looking into [these issues](https://github.com/model-checking/kani/contribute).
+
+In this chapter, we provide documentation that might be helpful for Kani
+developers (including external contributors):
+ 1. [Useful command-line instructions for Kani/CBMC/Git](./cheat-sheets.md).
+ 2. [Development setup recommendations for working with `rustc`](./rustc-hacks.md).
+ 3. [Guide for testing in Kani](./testing.md).
+
+> **NOTE:** The developer documentation is intended for Kani developers and not
+users. At present, the project is under heavy development and some items
+discussed in this documentation may stop working without notice (e.g., commands
+or configurations). Therefore, we recommend users to not rely on them.