Fix unsupported syntax in .manifest file

Fuchsia .manifest files do not support a `#` comment syntax. Because of this, if you copy and paste the current example code for this file, and then remove the line you don't need, you still see an error. To make this a bit easier to follow, split this into two code blocks, one for rustc, and one for cargo.

Author: diminishedprime

src/doc/rustc/src/platform-support/fuchsia.md

@@ -330,10 +330,18 @@ Now, create the following files inside:
 The `package` file describes our package's name and version number. Every
 package must contain one.
 
-**`pkg/hello_fuchsia.manifest`**
+**`pkg/hello_fuchsia.manifest` if using cargo**
 ```txt
-bin/hello_fuchsia=target/x86_64-fuchsia/debug/hello_fuchsia     # If using cargo...
-bin/hello_fuchsia=bin/hello_fuchsia                             # If using rustc...
+bin/hello_fuchsia=target/x86_64-fuchsia/debug/hello_fuchsia
+lib/ld.so.1=<SDK_PATH>/arch/x64/sysroot/dist/lib/ld.so.1
+lib/libfdio.so=<SDK_PATH>/arch/x64/dist/libfdio.so
+meta/package=pkg/meta/package
+meta/hello_fuchsia.cm=pkg/meta/hello_fuchsia.cm
+```
+
+**`pkg/hello_fuchsia.manifest` if using rustc**
+```txt
+bin/hello_fuchsia=bin/hello_fuchsia
 lib/ld.so.1=<SDK_PATH>/arch/x64/sysroot/dist/lib/ld.so.1
 lib/libfdio.so=<SDK_PATH>/arch/x64/dist/libfdio.so
 meta/package=pkg/meta/package