feat(examples): add source code view doc, add r/ README (#3163)

<!-- please provide a detailed description of the changes made in this
pull request. -->

## Description

Related to #3084

Adds a realm that teaches the user about the source code viewer in
`gnoweb`.

It also adds a `r/` root README.

<details><summary>Contributors' checklist...</summary>

- [x] Added new tests, or not needed, or not feasible
- [x] Provided an example (e.g. screenshot) to aid review or the PR is
self-explanatory
- [x] Updated the official documentation or not needed
- [x] No breaking changes were made, or a `BREAKING CHANGE: xxx` message
was included in the description
- [x] Added references to related issues and PRs
- [x] Provided any useful hints for running manual tests
</details>

---------

Co-authored-by: Morgan <[email protected]>

examples/gno.land/r/README.md

@@ -0,0 +1,10 @@
+# `r/`
+
+This directory primarily contains realms. It further branches out into namespaces:
+- `demo` - realms meant to demonstrate Gno functionality
+- `docs` - realms meant to teach about specific packages and concepts
+- `gnoland` - official gno.land realms
+- `gov` - governance realms
+- `sys` - system realms
+- `x` - experimental realms
+- `*` - can include personal namespaces, such as `manfred`, `leon`, etc.

examples/gno.land/r/docs/add/add.gno → examples/gno.land/r/docs/adder/adder.gno

@@ -1,4 +1,4 @@
-package add
+package adder
 
 import (
 	"strconv"

examples/gno.land/r/docs/add/add_test.gno → examples/gno.land/r/docs/adder/adder_test.gno

@@ -1,4 +1,4 @@
-package add
+package adder
 
 import (
 	"testing"
@@ -13,7 +13,7 @@ Current Number: 0
 
 Last Updated: Never
 
-[Increase Number](/r/docs/add$help&func=Add&n=42)
+[Increase Number](/r/docs/adder$help&func=Add&n=42)
 `
 	if output != expected {
 		t.Errorf("Initial Render failed, got:\n%s", output)
@@ -36,9 +36,9 @@ Current Number: 5
 
 Last Updated: 2009-02-13 23:31:30
 
-[Increase Number](/r/docs/add$help&func=Add&n=42)
+[Increase Number](/r/docs/adder$help&func=Add&n=42)
 `
 	if output != expected {
-		t.Errorf("Final Render failed, got:\n%s", output)
+		t.Errorf("Final Render failed, got:\n%s\nexpected:\n%s", output, finalOutput)
 	}
 }

examples/gno.land/r/docs/add/gno.mod → examples/gno.land/r/docs/adder/gno.mod

@@ -1,3 +1,3 @@
-module gno.land/r/docs/add
+module gno.land/r/docs/adder
 
 require gno.land/p/moul/txlink v0.0.0-latest

examples/gno.land/r/docs/home/home.gno

@@ -9,8 +9,9 @@ Explore various examples to learn more about Gno functionality and usage.
 ## Examples
 
 - [Hello World](/r/docs/hello) - A simple introductory example.
-- [Add](/r/docs/add) - An interactive example to update a number with transactions.
-- [AVL Pager](/r/docs/avl_pager) - Paginate through AVL tree items.
+- [Adder](/r/docs/adder) - An interactive example to update a number with transactions.
+- [Source](/r/docs/source) - View realm source code.
+- [AVL Pager](/r/docs/avl_pager) - Paginate through AVL tree items.  
 - ...
 
 ## Other resources

examples/gno.land/r/docs/source/gno.mod

@@ -0,0 +1 @@
+module gno.land/r/docs/source

examples/gno.land/r/docs/source/source.gno

@@ -0,0 +1,17 @@
+package source
+
+// Welcome to the source code of this realm!
+
+func Render(_ string) string {
+	return `# Viewing source code  
+gno.land makes it easy to view the source code of any pure
+package or realm, by using ABCI queries.
+
+gno.land's web frontend, ` + "`gnoweb`, " + ` makes this easy by
+providing a intuitive UI that fetches the source of the
+realm, that you can inspect anywhere by simply clicking
+on the [source] button.
+
+Check it out in the top right corner!
+`
+}