cmd/cover: more clearly mark as deprecated

Follow the conventions here:
https://github.com/golang/go/wiki/Deprecated. I wonder if we could just
delete it...

Change-Id: I6559bab0551304ff5e109a2dffd4ff86afba5203
Reviewed-on: https://go-review.googlesource.com/c/tools/+/234898
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Peter Weinberger <pjw@google.com>
diff --git a/cmd/cover/README b/cmd/cover/README
deleted file mode 100644
index ff9523d..0000000
--- a/cmd/cover/README
+++ /dev/null
@@ -1,2 +0,0 @@
-NOTE: For Go releases 1.5 and later, this tool lives in the
-standard repository. The code here is not maintained.
diff --git a/cmd/cover/README.md b/cmd/cover/README.md
new file mode 100644
index 0000000..62e6027
--- /dev/null
+++ b/cmd/cover/README.md
@@ -0,0 +1,3 @@
+# Deprecated
+
+NOTE: For Go releases 1.5 and later, this tool lives in the standard repository. The code here is not maintained.
diff --git a/cmd/cover/doc.go b/cmd/cover/doc.go
index b74d5b3..f903d85 100644
--- a/cmd/cover/doc.go
+++ b/cmd/cover/doc.go
@@ -6,6 +6,9 @@
 Cover is a program for analyzing the coverage profiles generated by
 'go test -coverprofile=cover.out'.
 
+Deprecated: For Go releases 1.5 and later, this tool lives in the
+standard repository. The code here is not maintained.
+
 Cover is also used by 'go test -cover' to rewrite the source code with
 annotations to track which parts of each function are executed.
 It operates on one Go source file at a time, computing approximate
@@ -17,11 +20,5 @@
 For usage information, please see:
 	go help testflag
 	go tool cover -help
-
-No longer maintained:
-
-For Go releases 1.5 and later, this tool lives in the
-standard repository. The code here is not maintained.
-
 */
 package main // import "golang.org/x/tools/cmd/cover"