docs: Initial CONTRIBUTING.md

CONTRIBUTING.md

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+# How to Contribute
+
+
+## ShellCheck
+
+For your contribution to be accepted, your changes need to pass
+ShellCheck.
+
+Run ShellCheck with the following command:
+
+```sh
+# Why do we exclude numerous tests?
+# See: https://github.com/dylanaraps/neofetch/wiki/Shellcheck-Exclusions
+shellcheck neofetch -e SC1090,SC2009,SC2012,SC2016,SC2034,SC2128,SC2153,SC2154,SC2178,SC2010,SC1004,SC1091,SC1117
+```
+
+**Note**: If you have trouble installing ShellCheck. You can open a pull
+request on the repo and our Travis.ci hook will run ShellCheck for you.
+
+
+## Coding Conventions
+
+- Indent 4 spaces.
+- Use [snake_case](https://en.wikipedia.org/wiki/Snake_case) for function
+  and variable names.
+- Keep lines below `100` characters long.
+- Use `[[ ]]` for tests.
+
+
+## No no's
+
+- Don’t use `bc`.
+- Don’t use `sed`.
+    - Use `bash`'s built-in [parameter expansion](http://wiki.bash-hackers.org/syntax/pe).
+- Don’t use `cat`.
+    - Use `bash`'s built-in syntax (`file="$(< /path/to/file.txt)")`).
+- Don’t use `grep "pattern" | awk '{ printf }'`.
+    - Use `awk '/pattern/ { printf }'`
+
+
+## If Statements
+
+If the test only has one command inside of it; use the compact `if`
+syntax. Otherwise the normal `if`/`fi` is just fine.
+
+```sh
+# Bad
+if [[ "$var" ]]; then
+    echo "$var"
+fi
+
+# Good
+[[ "$var" ]] && echo "$var"
+
+# Also good (Use this for longer lines.
+[[ "$var" ]] && \
+    echo "$var"
+```
+
+
+## Case Statements
+
+Case statements need to be formatted in a specific way.
+
+```sh
+# Good example (Notice the indentation).
+case "$var" in
+    1) echo 1 ;;
+    2)
+        echo 1
+        echo 2
+    ;;
+
+    *)
+        echo 1
+        echo 2
+        echo 3
+    ;;
+esac
+```