Document automatic installation behavior via rustup show

Author: 0xPoe

doc/src/overrides.md

@@ -19,7 +19,9 @@ the directory tree toward the filesystem root, and a `rust-toolchain.toml` file
 that is closer to the current directory will be preferred over a directory
 override that is further away.
 
-To verify which toolchain is active use `rustup show`.
+To verify which toolchain is active, you can use `rustup show`, 
+which will also try to install the corresponding
+toolchain if the current one has not been installed according to the above rules.
 
 [toolchain]: concepts/toolchains.md
 [toolchain override shorthand]: #toolchain-override-shorthand