Add BOM/STL Readme w/ links & info (#67)

* Create BOM/STL readme, add folder download link

Adds a readme to the "Assemblies BOM and STL" folder; Adds a small section that includes a link to the download-directory.github.io tool, which allows downloading the entire directory without downloading the repository or requiring a downloadable ZIP file. This tool zips the folder up automatically, and is client-side JavaScript powered.

* Add CAD link to BOM/STL readme

* Print settings, part quantity/explanation BOM/STL readme

* Typography (folder download italics)

Assemblies BOM and STL/readme.md

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+# Assembly BOM's and STL's
+
+This folder contains the BOM and STL files for each individual assembly specified in the [CAD](/CAD) folder.
+
+You can explore the folders for the assemblies you are interested in, or [download this folder](https://download-directory.github.io/?url=https://github.com/VzBoT3D/VzBoT-Vz330/tree/master/Assemblies%20BOM%20and%20STL) in full *(powered by the "download-directory.github.io" tool)*.
+
+## Printing
+
+Settings for printing can be found on the [Print settings](https://docs.vzbot.org/general/misc-info/print-settings/) VzBoT Docs page.
+
+The quantity of each printed part may differ. A selection of parts are available in different variants to suit the needs of more than one possible BOM or hardware setup. These are mostly supplied for retro-compatibility, and no longer recommended for new builds. New builds are encouraged to follow the standard BOM, like the Mellow3D kits. 
+
+Please carefully read through the filenames to assess whether the file or part applies to your machine or not.