faq: add a question about supported toolchains

Signed-off-by: Julian Stecklina <[email protected]>

Author: Julian Stecklina

FAQ.md

@@ -72,6 +72,19 @@ Firecracker supports Linux host and guest operating systems with kernel versions
 4.14 and above. The long-term support plan is still under discussion. A leading
 option is to support Firecracker for the last two Linux stable branch releases.
 
+### What toolchains are supported by Firecracker?
+
+The toolchain that Firecracker is tested against and that is recommended for
+building production releases is the one that is automatically used by building
+Firecracker using `devtool` (see [README](README.md)). In this configuration,
+Firecracker is currently built as a static binary linked against
+the [musl](https://www.musl-libc.org/) libc implementation.
+
+Firecracker also builds using [glibc](https://www.gnu.org/software/libc/)
+toolchains, such as the default Rust toolchains provided in certain Linux
+distributions. That being said, Firecracker binaries built without `devtool` are
+always considered experimental and should not be used in production.
+
 ### What is the open source license for Firecracker?
 
 Firecracker is licensed under the Apache License, version 2.0, allowing you to