Document debuginfo defaults and link to rustc's docs

Co-authored-by: Scott Schafer <[email protected]>

src/doc/src/reference/profiles.md

@@ -67,11 +67,13 @@ amount of debug information included in the compiled binary.
 
 The valid options are:
 
-* `0`, `false`, or `"none"`: no debug info at all
+* `0`, `false`, or `"none"`: no debug info at all, default for [`release`](https://doc.rust-lang.org/cargo/reference/profiles.html#release)
 * `"line-directives-only"`: line info directives only. For the nvptx* targets this enables [profiling](https://reviews.llvm.org/D46061). For other use cases, `line-tables-only` is the better, more compatible choice.
 * `"line-tables-only"`: line tables only. Generates the minimal amount of debug info for backtraces with filename/line number info, but not anything else, i.e. no variable or function parameter info.
 * `1` or `"limited"`: debug info without type or variable-level information. Generates more detailed module-level info than `line-tables-only`.
-* `2`, `true`, or `"full"`: full debug info
+* `2`, `true`, or `"full"`: full debug info, default for [`dev`](https://doc.rust-lang.org/cargo/reference/profiles.html#dev)
+
+For more information on what each option does see `rustc`'s docs on [debuginfo](https://doc.rust-lang.org/rustc/codegen-options/index.html#debuginfo)
 
 You may wish to also configure the [`split-debuginfo`](#split-debuginfo) option
 depending on your needs as well.