Document configurable block models. (#99)

* Document configurable block models.

Closes #97

* Follow style guide

* Fix info block.

* Downgrade pyyaml.

---------

Co-authored-by: Peregrine05 <92183530+Peregrine05@users.noreply.github.com>

ChunkyDocs/docs/support/minecraft_compatibility.md

@@ -23,4 +23,18 @@ Below is a list of the Minecraft versions currently supported by Chunky and ever
 | Campfire with items         | Not supported  | Not supported           | In development             | #1704                          |
 | Armor trims                 | Not supported  | Planned                 | Planned                    | #1708                          |
 
+## Block models
+
+Mojang sometimes changes the block models or textures (and texture mappings) of existing blocks. By default, Chunky uses the *latest* block models of Java Edition.
+
+To maintain compatibility with old resource packs, there are flags to switch to older block models. These flags can be specified in the Launcher as <samp>Java options</samp>, eg. `-Dchunky.blockModels.cocoa=pre-1.19` to switch to the old cocoa plant model.
+
+| Block | Flag                       | Values                       | Note                                                                                                                                     |
+| ----- | -------------------------- | ---------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------- |
+| cocoa | `chunky.blockModels.cocoa` | `1.19` (default), `pre-1.19` | Block model changed in 1.19; stage 2 cocoa plant is displayed incorrectly when the resource pack and block model don't match (see #1761) |
+
+!!! info "Unsupported block models"
+
+    If you're missing an old block model or encounter issues with a block when using a resource pack that is made for an older Minecraft version, please [create an issue](https://github.com/chunky-dev/chunky/issues/new/choose). We will add support for all block models that are present in release versions of Minecraft (ie. block models that only appeared in snapshots will not be supported).
+
 --8<-- "includes/abbreviations.md"

requirements.txt

@@ -11,7 +11,7 @@ mkdocs==1.6.1
 mkdocs-macros-plugin==1.0.4
 mkdocs-material==9.5.35
 nltk==3.6.2
-PyYAML==6.0
+PyYAML==5.3.1
 regex==2022.4.24
 six==1.16.0
 tornado==6.1