List the varsets in the README.

Author: artob

README.md

@@ -25,6 +25,14 @@
 cargo add getenv
 ```
 
+```toml
+getenv = 0.1
+```
+
+```toml
+getenv = { version = "0.1", default-features = false, features = ["posix"] }
+```
+
 ## 👉 Examples
 
 ### Importing the library
@@ -33,9 +41,41 @@ cargo add getenv
 use getenv::*;
 ```
 
+### Reading environment variables
+
+```rust
+use getenv::aws::*;
+
+println!("aws_access_key_id = {:?}", aws_access_key_id())
+println!("aws_secret_access_key = {:?}", aws_secret_access_key())
+```
+
 ## 📚 Reference
 
-TBD
+```rust
+use getenv::aws::*;
+use getenv::cargo::*;
+use getenv::conda::*;
+use getenv::cuda::*;
+use getenv::docker::*;
+use getenv::git::*;
+use getenv::go::*;
+use getenv::homebrew::*;
+use getenv::java::*;
+use getenv::locale::*;
+use getenv::macos::*;
+use getenv::near::*;
+use getenv::node::*;
+use getenv::openssl::*;
+use getenv::posix::*;
+use getenv::proxy::*;
+use getenv::python::*;
+use getenv::ruby::*;
+use getenv::rust::*;
+use getenv::ssh::*;
+use getenv::windows::*;
+use getenv::xdg::*;
+```
 
 ## 👨‍💻 Development
 

Rakefile

@@ -28,6 +28,14 @@ namespace :varset do
       puts %{pub use #{varset}::*;}
     end
   end
+
+  task :readme do
+    puts %{Varset | Feature | Reference}
+    puts %{------ | ------- | ---------}
+    varsets.each do |varset|
+      puts %{#{varset} | `#{varset}` | [`use getenv::#{varset}::*;`](https://docs.rs/getenv/latest/getenv/varsets/#{varset}/index.html)}
+    end
+  end
 end
 
 def varsets