Soft deprecate webrick and add some details as to why.

rackup.gemspec

@@ -23,8 +23,8 @@ Gem::Specification.new do |spec|
   }
 
   spec.add_dependency "rack", ">= 3"
-  spec.add_dependency "webrick", "~> 1.8"
-
+
+  spec.add_development_dependency "webrick", "~> 1.8"
   spec.add_development_dependency "bundler"
   spec.add_development_dependency "minitest", "~> 5.0"
   spec.add_development_dependency "minitest-global_expectations"

readme.md

@@ -1,13 +1,17 @@
 # Rackup
 
-`rackup` provides a command line interface for running a Rack-compatible application.
+`rackup` provides a command line interface for running a Rack-compatible application. It also provides a generic interface for starting a `rack`-compatible server: `Rackup::Handler`. It is not designed for production use.
 
 [![Development Status](https://github.com/rack/rackup/workflows/Test/badge.svg)](https://github.com/rack/rackup/actions?workflow=Test)
 
 ## Installation
 
 ``` bash
-$ gem install rackup
+-- For Falcon
+$ gem install rackup falcon
+
+-- For Puma
+$ gem install rackup puma
 ```
 
 ## Usage
@@ -20,6 +24,35 @@ $ rackup
 
 Your application should now be available locally, typically `http://localhost:9292`.
 
+## (Soft) Deprecation
+
+For a long time, `rackup` (the executable and implementation) was part of `rack`, and `webrick` was the default server, included with Ruby. It made it easy to run a Rack application without having to worry about the details of the server - great for documentation and demos.
+
+When `webrick` was removed from the Ruby standard library, `rack` started depending on `webrick` as a default server. Every web application and server would pull in `webrick` as a dependency, even if it was not used. To avoid this, the `rackup` component of `rack` was moved to this gem, which depended on `webrick`.
+
+However, many libraries (e.g. `rails`) still depend on `rackup` and end up pulling in `webrick` as a dependency. To avoid this, the decision was made to cut `webrick` as a dependency of `rackup`. This means that `rackup` no longer depends on `webrick`, and you need to install it separately if you want to use it.
+
+As a consequence of this, the value of the `rackup` gem is further diminished. In other words, why would you do this:
+
+``` bash
+$ gem install rackup puma
+$ rackup ...
+```
+
+when you can do this:
+
+``` bash
+$ gem install puma
+$ puma ...
+```
+
+In summary, the maintainers of rack recommend the following:
+
+- Libraries should not depend on `rackup` if possible. `rackup` as an executable made sense when webrick shipped with Ruby, so there was always a fallback. But that hasn't been true since Ruby 3.0.
+- Frameworks and applications should focus on providing `config.ru` files, so that users can use the webserver program of their choice directly (e.g. puma, falcon). 
+- There is still some value in the generic `rackup` and `Rackup::Handler` interfaces, but we encourage users to invoke the server command directly if possible.
+- Webrick should be avoided if possible.
+
 ## Contributing
 
 We welcome contributions to this project.