Replace jqplay.org with play.jqlang.org (#3265)

As discussed in https://github.com/jqlang/jq/discussions/3244, we are
moving jqplay to the jqlang GitHub organization. This updates all
references from jqplay.org to play.jqlang.org.

README.md

@@ -5,7 +5,7 @@
 ## Documentation
 
 - **Official Documentation**: [jqlang.org](https://jqlang.org)
-- **Try jq Online**: [jqplay.org](https://jqplay.org)
+- **Try jq Online**: [play.jqlang.org](https://play.jqlang.org)
 
 ## Installation
 
@@ -17,13 +17,16 @@ Download the latest releases from the [GitHub release page](https://github.com/j
 
 Pull the [jq image](https://github.com/jqlang/jq/pkgs/container/jq) to start quickly with Docker.
 
-
 #### Run with Docker
+
 ##### Example: Extracting the version from a `package.json` file
+
 ```bash
 docker run --rm -i ghcr.io/jqlang/jq:latest < package.json '.version'
 ```
+
 ##### Example: Extracting the version from a `package.json` file with a mounted volume
+
 ```bash
 docker run --rm -i -v "$PWD:$PWD" -w "$PWD" ghcr.io/jqlang/jq:latest '.version' package.json
 ```