PlayerMetaData: Import from minetest_docs

pages/PlayerMetaData.md

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+PlayerMetaData is a per-world, per-player persistent string key-value store implementing all methods of [[MetaData]].
+
+The granularity of the persisted snapshots is determined by the `map_save_interval` setting.
+
+NOTE: Since PlayerMetaData is shared across all mods,
+it is considered good practice to prefix the keys set by your mod with your mod name plus a delimiter
+such as `:` to avoid collisions: The `score` field of a quest mod and a mobs mod f.E. might
+be called `fancy_quests:score` and `fancy_mobs:score` respectively.
+
+## `player:get_meta()`
+Used to obtain a mutable PlayerMetaData reference.
+
+### Arguments
+- `player`: A valid Player object
+
+NOTE: Minetest requiring a valid `player` object means PlayerMetaData is only accessible
+while players are online; if you need per-player storage while players are offline,
+you can use ModStorage and save either a serialized table per-player or concatenate
+the keys of the per-player entries with the playername using a delimiter.
+Reusing the above example, `fancy_quests:score` might be stored as `<playername>:score`
+or as key-value pair with key `<playername>` and value `minetest.write_json{score = ...}`
+(or `minetest.serialize`)  in ModStorage.
+
+A [feature request](https://github.com/minetest/minetest/issues/6193)
+to make PlayerMetaData available for offline players exists;
+
+### Returns
+- `meta` - PlayerMetaData: Public & shared PlayerMetaData object for the player