slog-handler-guide: fix typo, tweak phrasing

Fix one typo and improve the clarity and phrasing of some prose.

Change-Id: I4cec5b052df0d33f6e4a3f2751313b3c1d59ae2c
Reviewed-on: https://go-review.googlesource.com/c/example/+/636275
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Alan Donovan <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>

slog-handler-guide/guide.md

@@ -15,7 +15,7 @@ The standard library’s `log/slog` package has a two-part design.
 A "frontend," implemented by the `Logger` type,
 gathers structured log information like a message, level, and attributes,
 and passes them to a "backend," an implementation of the `Handler` interface.
-The package comes with two built-in handlers that usually should be adequate.
+The package comes with two built-in handlers that should usually be adequate.
 But you may need to write your own handler, and that is not always straightforward.
 This guide is here to help.
 
@@ -28,7 +28,7 @@ types work together.
 Each logger contains a handler. Certain `Logger` methods do some preliminary work,
 such as gathering key-value pairs into `Attr`s, and then call one or more
 `Handler` methods. These `Logger` methods are `With`, `WithGroup`,
-and the output methods.
+and the output methods like `Info`, `Error` and so on.
 
 An output method fulfills the main role of a logger: producing log output.
 Here is a call to an output method:
@@ -314,7 +314,7 @@ Most of the fields of `IndentHandler` can be copied shallowly, but the slice of
 the same underlying array. If we used `append` instead of making an explicit
 copy, we would introduce that subtle aliasing bug.
 
-Using `withGroupOrAttrs`, the `With` methods are easy:
+The `With` methods are easy to write using `withGroupOrAttrs`:
 
 %include indenthandler2/indent_handler.go withs -
 
@@ -362,7 +362,7 @@ See [this bug report](https://go.dev/issue/61321) for more detail.
 
 ### With pre-formatting
 
-Our second implementation implements pre-formatting.
+Our second version of the `WithGroup` and `WithAttrs` methods provides pre-formatting.
 This implementation is more complicated than the previous one.
 Is the extra complexity worth it?
 That depends on your circumstances, but here is one circumstance where
@@ -410,7 +410,7 @@ We also need to track how many groups we've opened, which we can do
 with a simple counter, since an opened group's only effect is to change the
 indentation level.
 
-The `WithGroup` implementation is a lot like the previous one: just remember the
+This `WithGroup` is a lot like the previous one: it just remembers the
 new group, which is unopened initially.
 
 %include indenthandler3/indent_handler.go WithGroup -
@@ -571,7 +571,7 @@ impossible to inspect a system, as is typically the case with a production
 server, logs provide the most detailed way to understand its behavior.
 Therefore, your handler should be robust to bad input.
 
-For example, the usual advice when when a function discovers a problem,
+For example, the usual advice when a function discovers a problem,
 like an invalid argument, is to panic or return an error.
 The built-in handlers do not follow that advice.
 Few things are more frustrating than being unable to debug a problem that