docs: fix warnings and use warning note

Fixes:
```
warning: redundant explicit link target
   --> binrw/src/../doc/attribute.md:120:85
    |
120 | | rw  | [`try_calc`](#calculations) | field | Like `calc`, but
returns a [`Result`](Result).
    |
--------  ^^^^^^ explicit target is redundant
    |
|
    |
because label contains path that resolves to same destination
    |
    = note: when a link's destination is not specified,
            the label is used to resolve intra-doc links
    = note: `#[warn(rustdoc::redundant_explicit_links)]` on by default
help: remove explicit link target
    |
120 | | rw  | [`try_calc`](#calculations) | field | Like `calc`, but
returns a [`Result`].
    |
~~~~~~~~~~

warning: redundant explicit link target
   --> binrw/src/../doc/attribute.md:121:92
    |
121 | | rw  | [`try_map`](#map) | all except unit variant | Like `map`,
but returns a [`Result`](Result).
    |
--------  ^^^^^^ explicit target is redundant
    |
|
    |
because label contains path that resolves to same destination
    |
    = note: when a link's destination is not specified,
            the label is used to resolve intra-doc links
help: remove explicit link target
    |
121 | | rw  | [`try_map`](#map) | all except unit variant | Like `map`,
but returns a [`Result`].
    |
~~~~~~~~~~

warning: redundant explicit link target
    --> binrw/src/../doc/attribute.md:1520:13
     |
1520 | [`Default`](core::default::Default) instead of reading data from
the reader:
     |  ---------  ^^^^^^^^^^^^^^^^^^^^^^ explicit target is redundant
     |  |
     |  because label contains path that resolves to same destination
     |
     = note: when a link's destination is not specified,
             the label is used to resolve intra-doc links
help: remove explicit link target
     |
1520 | [`Default`] instead of reading data from the reader:
     | ~~~~~~~~~~~

warning: `binrw` (lib doc) generated 3 warnings
```

binrw/doc/attribute.md

@@ -117,8 +117,8 @@ Glossary of directives in binrw attributes (`#[br]`, `#[bw]`, `#[brw]`).
 | rw  | [`stream`](#stream-access-and-manipulation) | struct, non-unit enum, unit-like enum | Exposes the underlying <span class="br">read</span><span class="bw">write</span> stream.
 | r   | [`temp`](#temp) | field | Uses a field as a temporary variable. Only usable with the [`binread`](macro@crate::binread) attribute macro.
 | r   | [`try`](#try) | field | Tries to parse and stores the [`default`](core::default::Default) value for the type if parsing fails instead of returning an error.
-| rw  | [`try_calc`](#calculations) | field | Like `calc`, but returns a [`Result`](Result).
-| rw  | [`try_map`](#map) | all except unit variant | Like `map`, but returns a [`Result`](Result).
+| rw  | [`try_calc`](#calculations) | field | Like `calc`, but returns a [`Result`].
+| rw  | [`try_map`](#map) | all except unit variant | Like `map`, but returns a [`Result`].
 |  w  | [`write_with`](#custom-parserswriters) | field | Specifies a custom function for writing a field.
 
 [*]: #terminology
@@ -947,13 +947,17 @@ object.write(&mut output)
 
 <div class="bw">
 
+<div class="warning">
+
 **These directives can only be used with [`binwrite`](macro@crate::binwrite).
 They will not work with `#[derive(BinWrite)]`.**
 
 **When using these directives, the `#[binwrite]` attribute must be placed
 *before* other attributes like `#[derive(Debug)]`. Otherwise, the other
 attributes will generate code that references non-existent fields, and
 compilation will fail.**
+
+</div>
 </div>
 
 The `calc` and `try_calc` directives compute the value of a field instead of
@@ -1517,7 +1521,7 @@ if let binrw::Error::NoVariantMatch { pos } = error {
 
 For [`BinRead`](crate::BinRead), the `ignore` directive, and its alias
 `default`, sets the value of the field to its
-[`Default`](core::default::Default) instead of reading data from the reader:
+[`Default`] instead of reading data from the reader:
 
 ```text
 #[br(default)] or #[br(ignore)]
@@ -2663,13 +2667,17 @@ assert_eq!(out.into_inner(), b"\x01\x03\0\x04\x01");
 
 # Temp
 
+<div class="warning">
+
 **This directive can only be used with [`binread`](macro@crate::binread). It
 will not work with `#[derive(BinRead)]`.**
 
 **When using `#[br(temp)]`, the `#[binread]` attribute must be placed *before*
 other attributes like `#[derive(Debug)]`. Otherwise, the other attributes will
 generate code that references non-existent fields, and compilation will fail.**
 
+</div>
+
 The `temp` directive causes a field to be treated as a temporary variable
 instead of an actual field. The field will be removed from the struct
 definition generated by [`binread`](macro@crate::binread):