cmd/gogio: rename the gio too to gogio

The `gio` name clashes with a widely deployed GNOME tool.
Rename our tool to `gogio`, "the go tool for gio programs".

Fixes gio#20

Signed-off-by: Elias Naur <mail@eliasnaur.com>

cmd/gogio/doc.go

@@ -0,0 +1,10 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+/*
+The gogio tool builds and packages Gio programs for Android, iOS/tvOS
+and WebAssembly.
+
+Run gogio with no arguments for instructions, or see the examples at
+https://gioui.org.
+*/
+package main