Add since info to recently added env vars (#15458)

Author: sabiwara

lib/mix/lib/mix.ex

@@ -356,12 +356,12 @@ defmodule Mix do
     * `MIX_INSTALL_DIR` *(since v1.12.0)* - specifies directory where `Mix.install/2` keeps
        install cache
 
-    * `MIX_OS_CONCURRENCY_LOCK` - when set to `0` or `false`, disables mix compilation locking.
+    * `MIX_OS_CONCURRENCY_LOCK` *(since v1.18.2)* - when set to `0` or `false`, disables mix compilation locking.
       While not recommended, this may be necessary in cases where hard links or TCP sockets are
       not available. When opting for this behaviour, make sure to not start concurrent compilations
       of the same project
 
-    * `MIX_OS_DEPS_COMPILE_PARTITION_COUNT` - when set to a number greater than 1, it enables
+    * `MIX_OS_DEPS_COMPILE_PARTITION_COUNT` *(since v1.19.0)* - when set to a number greater than 1, it enables
       compilation of dependencies over multiple operating system processes. See `mix help deps.compile`
       for more information