autodiff: update formating, improve examples for the unstable-book

Author: ZuseZ4

src/doc/unstable-book/src/compiler-flags/autodiff.md

@@ -6,16 +6,37 @@ The tracking issue for this feature is: [#124509](https://github.com/rust-lang/r
 
 This feature allows you to differentiate functions using automatic differentiation.
 Set the `-Zautodiff=<options>` compiler flag to adjust the behaviour of the autodiff feature.
-Multiple options can be separated with a comma. Valid options are:
-
-`Enable` - Required flag to enable autodiff
-`PrintTA` - print Type Analysis Information
-`PrintTAFn` - print Type Analysis Information for a specific function
-`PrintAA` - print Activity Analysis Information
-`PrintPerf` - print Performance Warnings from Enzyme
-`PrintSteps` - prints all intermediate transformations
-`PrintModBefore` - print the whole module, before running opts
-`PrintModAfter` - print the module after Enzyme differentiated everything
-`LooseTypes` - Enzyme's loose type debug helper (can cause incorrect gradients)
-`Inline` - runs Enzyme specific Inlining
-`RuntimeActivity` - allow specifying activity at runtime
+Multiple options can be separated with a comma. 
+
+# Syntax
+```bash
+rustc -Z autodiff=Enable[,options]
+```
+
+Where `options` can be:
+
+`Enable` - Required flag to enable autodiff  
+`PrintTA` - print Type Analysis Information  
+`PrintTAFn` - print Type Analysis Information for a specific function (consider combining it with `no_mangle`)  
+`PrintAA` - print Activity Analysis Information  
+`PrintPerf` - print Performance Warnings from Enzyme  
+`PrintSteps` - prints all intermediate transformations  
+`PrintModBefore` - print the whole module, before running opts  
+`PrintModAfter` - print the module after Enzyme differentiated everything  
+`LooseTypes` - Enzyme's loose type debug helper (can cause incorrect gradients)  
+`Inline` - runs Enzyme specific Inlining  
+`RuntimeActivity` - allow specifying activity at runtime  
+
+
+# Examples
+
+```bash
+# Enable autodiff via cargo, assuming `enzyme` being a toolchain that supports autodiff
+"RUSTFLAGS=-Zautodiff=Enable" cargo +enzyme build
+
+# Enable autodiff directly via rustc
+rustc -Z autodiff=Enable
+
+# Print TypeAnalysis updates for the function `foo`, as well as Activity Analysis for all differentiated code.
+rustc -Z autodiff=Enable,PrintTAFn=foo,PrintAA
+```