make furnace discord server

sure

CONTRIBUTING.md

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+# Contributing
+
+contributions to Furnace are welcome!
+
+# Getting ready
+
+log into your Github account, and click the Fork button in the header of the project's page.
+
+then open a terminal and clone your fork:
+
+```
+git clone git@github.com:USERNAME/furnace.git
+```
+
+(replace `USERNAME` with your username)
+
+# Working
+
+## Code
+
+bug fixes, improvements and several other things accepted.
+
+the coding style is described here:
+
+- indentation: two spaces
+- modified 1TBS style:
+  - no spaces in function calls
+  - spaces between arguments in function declarations
+  - no spaces in operations except for `||` and `&&`
+  - no space between variable name and assignment
+  - space between macro in string literals
+  - C++ pointer style: `void* variable` rather than `void *variable`
+  - indent switch cases
+  - preprocessor directives not intended
+  - if macro comprises more than one line, indent
+
+some files (particularly the ones in `src/engine/platform/sound` and `extern/`) don't follow this style.
+
+you don't have to follow this style. I will fix it after I accept your contribution.
+
+## Demo Songs
+
+just put your demo song in `demos/`!
+
+# Finishing
+
+after you've done your modifications, commit the changes and push.
+then open your fork on GitHub and send a pull request.
+
+# I don't know how to use Git but I want to contribute with a demo song
+
+you can also contact me directly! [find me here.](https://tildearrow.org/?p=contact)