rails: create README (#5841)

plugins/rails/README.md

+# Rails
+
+This plugin adds completion for [Ruby On Rails Framework](https://rubyonrails.org/) and [Rake](https://ruby.github.io/rake/) commands, as well as some aliases for logs and environment variables.
+
+To use it, add `rails` to the plugins array in your zshrc file:
+
+```zsh
+plugins=(... rails)
+```
+
+## List of Aliases
+
+### Rails aliases
+
+| Alias | Command                    | Description                                        |
+|-------|----------------------------|----------------------------------------------------|
+| `rc`  | `rails console`            | Interact with your Rails app from the CLI          |
+| `rcs` | `rails console --sandbox`  | Test code in a sandbox, without changing any data  |
+| `rd`  | `rails destroy`            | Undo a generate operation                          |
+| `rdb` | `rails dbconsole`          | Interact with your db from the console             |
+| `rg`  | `rails generate`           | Generate boilerplate code                          |
+| `rgm` | `rails generate migration` | Generate a db migration                            |
+| `rp`  | `rails plugin`             | Run a Rails plugin command                         |
+| `ru`  | `rails runner`             | Run Ruby code in the context of Rails              |
+| `rs`  | `rails server`             | Launch a web server                                |
+| `rsd` | `rails server --debugger`  | Launch a web server with debugger                  |
+| `rsp` | `rails server --port`      | Launch a web server and specify the listening port |
+
+### Rake aliases
+
+| Alias   | Command                         | Description                                            |
+|---------|---------------------------------|--------------------------------------------------------|
+| `rdm`   | `rake db:migrate`               | Run pending db migrations                              |
+| `rdms`  | `rake db:migrate:status`        | Show current db migration status                       |
+| `rdmtc` | `rake db:migrate db:test:clone` | Run pending migrations and clone db into test database |
+| `rdr`   | `rake db:rollback`              | Roll back the last migration                           |
+| `rdc`   | `rake db:create`                | Create the database                                    |
+| `rds`   | `rake db:seed`                  | Seed the database                                      |
+| `rdd`   | `rake db:drop`                  | Delete the database                                    |
+| `rdrs`  | `rake db:reset`                 | Delete the database and set it up again                |
+| `rdtc`  | `rake db:test:clone`            | Clone the database into the test database              |
+| `rdtp`  | `rake db:test:prepare`          | Duplicate the db schema into your test database        |
+| `rdsl`  | `rake db:schema:load`           | Load the database schema                               |
+| `rlc`   | `rake log:clear`                | Clear Rails logs                                       |
+| `rn`    | `rake notes`                    | Search for notes (`FIXME`, `TODO`) in code comments    |
+| `rr`    | `rake routes`                   | List all defined routes                                |
+| `rrg`   | `rake routes | grep`            | List and filter the defined routes                     |
+| `rt`    | `rake test`                     | Run Rails tests                                        |
+| `rmd`   | `rake middleware`               | Interact with Rails middlewares                        |
+| `rsts`  | `rake stats`                    | Print code statistics                                  |
+
+### Utility aliases
+
+| Alias     | Command                       | Description                                    |
+|-----------|-------------------------------|------------------------------------------------|
+| `devlog`  | `tail -f log/development.log` | Show and follow changes to the development log |
+| `prodlog` | `tail -f log/production.log`  | Show and follow changes to the production log  |
+| `testlog` | `tail -f log/test.log`        | Show and follow changes to the test log        |
+
+### Environment settings
+
+| Alias | Command                 | Description                     |
+|-------|-------------------------|---------------------------------|
+| `RED` | `RAILS_ENV=development` | Sets `RAILS_ENV` to development |
+| `REP` | `RAILS_ENV=production`  | Sets `RAILS_ENV` to production  |
+| `RET` | `RAILS_ENV=test`        | Sets `RAILS_ENV` to test        |
+
+These are global aliases. Use in combination with a command or just run them
+separately. For example: `RED rake db:migrate` will migrate the production db.
+
+### Legacy stuff
+
+| Alias   | Command                            |
+|---------|------------------------------------|
+| `sstat` | `thin --stats "/thin/stats" start` |
+| `sg`    | `ruby script/generate`             |
+| `sd`    | `ruby script/destroy`              |
+| `sp`    | `ruby script/plugin`               |
+| `sr`    | `ruby script/runner`               |
+| `ssp`   | `ruby script/spec`                 |
+| `sc`    | `ruby script/console`              |
+| `sd`    | `ruby script/server --debugger`    |
+