Merge pull request 'Add how to play notes' (#3341) from add_download_notes into master

Reviewed-on: https://git.minetest.land/MineClone2/MineClone2/pulls/3341

HOW_TO_PLAY.md

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+Survive, farm, build, explore, play with friends, and do much more. Inspired by a well known block game, pushing beyond.
+
+How to play:
+
+#### Download Minetest
+- Navigate to https://www.minetest.net/ to download the client.
+- Once installed, open and select the "Content" tab
+
+#### Install MineClone2 from ContentDB
+- Click "Browse Online Content" and filter by Games (select "Games" from the dropdown box)
+- Find "MineClone2" (should be first on the list or on the first page)
+- Click the [+] button next to MineClone2 and wait for download to finish
+- Click "Back to Main Menu"
+
+#### Create new world and play
+- Click "Start Game" tab
+- At the bottom click the MineClone2 icon (the 2 dirt with grass blocks)
+- Click "New", give your world a name
+- You can leave seed blank or put in a word of your choice
+- Select your new world
+- Click "Play Game" and enjoy!