regexp: fix copy-paste typo on Regexp.UnmarshalText doc

I noticed that https://go.dev/cl/479401 called both methods MarshalText
in the godoc, so fix that.

While here, add more godoc links for better usability.

Change-Id: I8f10bafeca6a1ca1c1ed9be7a7dd9fdecfe991a0
Reviewed-on: https://go-review.googlesource.com/c/go/+/484335
Auto-Submit: Ian Lance Taylor <iant@google.com>
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Reviewed-by: David Chase <drchase@google.com>

src/regexp/regexp.go

@@ -1284,18 +1284,18 @@ func (re *Regexp) Split(s string, n int) []string {
 	return strings
 }
 
-// MarshalText implements the encoding.TextMarshaler interface. The output
+// MarshalText implements [encoding.TextMarshaler]. The output
 // matches that of calling the [Regexp.String] method.
 //
 // Note that the output is lossy in some cases: This method does not indicate
-// POSIX regular expressions (i.e. those compiled by calling CompilePOSIX), or
+// POSIX regular expressions (i.e. those compiled by calling [CompilePOSIX]), or
 // those for which the [Regexp.Longest] method has been called.
 func (re *Regexp) MarshalText() ([]byte, error) {
 	return []byte(re.String()), nil
 }
 
-// MarshalText implements the encoding.TextUnmarshaler interface by calling
-// Compile on the encoded value.
+// UnmarshalText implements [encoding.TextUnmarshaler] by calling
+// [Compile] on the encoded value.
 func (re *Regexp) UnmarshalText(text []byte) error {
 	newRE, err := Compile(string(text))
 	if err != nil {