Update README with misc_docs dir

Author: ryyppy

README.md

@@ -58,6 +58,7 @@ build specific pages (file `index_data/x.json` not found).
 - `data`: Contains hand-curated data, such as sidebar ordering, blog data, etc
 - `index_data`: Contains generated data, usually generated by scripts like `scripts/extract-tocs.js`
 - `compilers`: Contains a subdirectory with independently installed ReScript compilers, to be able to compile / test examples with different ReScript versions
+- `misc_docs`: Contains `pages` independent resources that are embedded in miscellaneous pages (e.g. for the syntax lookup)
 - `pages`: All Next pages. Those are written in JS / MDX, some pages are re-exporting ReScript based pages from the `src/` directory.
 - `styles`: Contains all extra CSS that cannot be expressed with Tailwind
 - `src`: Contains all ReScript related code for the UI. Within `src`, you will also find all ReScript based Next pages that are re-exported in the `pages` directory