Merge #142 #151

142: Update qemu.md r=korken89 a=flip111

Add link to qemu wiki. As proof and also interested reader can see other architectures too.

151: Update exceptions.md r=korken89 a=flip111

that it's marked with `*  *` already makes it have special significance. Let's link to an explanation

Co-authored-by: flip111 <flip101@gmail.com>

src/start/exceptions.md

@@ -37,7 +37,7 @@ fn SysTick() {
 ```
 
 As you may know, using `static mut` variables in a function makes it
-*non-reentrant*. It's undefined behavior to call a non-reentrant function,
+[*non-reentrant*](https://en.wikipedia.org/wiki/Reentrancy_(computing)). It's undefined behavior to call a non-reentrant function,
 directly or indirectly, from more than one exception / interrupt handler or from
 `main` and one or more exception / interrupt handlers.
 

src/start/qemu.md

@@ -1,7 +1,7 @@
 # QEMU
 
 We'll start writing a program for the [LM3S6965], a Cortex-M3 microcontroller.
-We have chosen this as our initial target because it can be emulated using QEMU
+We have chosen this as our initial target because it [can be emulated](https://wiki.qemu.org/Documentation/Platforms/ARM#Supported_in_qemu-system-arm) using QEMU
 so you don't need to fiddle with hardware in this section and we can focus on
 the tooling and the development process.