add build-from-source info to Tests architecture docs

it's mentioned in the README, but it's worth mentioning again in the
Tests section of the architecture doc.

diff --git a/ARCHITECTURE.md b/ARCHITECTURE.md
index 1b8577f76d2ddec3964d6b731573a9ce0dcd9da8..b749218c3495004d7a95d4aca47630ea646c38f7 100644 (file)
--- a/ARCHITECTURE.md
+++ b/ARCHITECTURE.md
@@ -103,6 +103,9 @@ assert_that(
 );
 ```
 
+Alternatively to build and run a custom version of cargo simply run `cargo build`
+and execute `target/debug/cargo`.
+
 ## Logging
 
 Cargo uses [`env_logger`](https://docs.rs/env_logger/*/env_logger/), so you can set