Add contributing guidelines

CONTRIBUTING.md

@@ -0,0 +1,58 @@
+## Contributing to Sol
+
+Looking to contribute to Sol? Well, first thing I want to mention is thank you!
+Second of all, this is probably where you should look :)
+
+## Reporting Issues
+
+If you found a bug, please make sure to make an issue in the issue tracker.
+
+The guidelines for reporting a bug are relatively simple and are as follows:
+
+1. Produce a simple, short, compilable test case that reproduces your problem.
+2. Make a descriptive title that summarises the bug as a whole.
+3. Explain the bug in as much detail as you can in the body of the issue.
+
+If you have all of those requirements set, then your issue reporting is golden. 
+
+## Submitting a pull request
+
+Submitting a pull request is fairly simple, just make sure it focuses on a single aspect and doesn't 
+manage to have scope creep and it's probably good to go. It would be incredibly lovely if the style is 
+consistent to those found in the repository.
+
+They are as follows (more will be added as they come up):
+
+- No spaces between parentheses. e.g. `f(g())` not `f ( g ( ) )`.
+- No tabs allowed. Use 4 space indentation.
+- Bracing style is
+
+```cpp
+if(my_bool) {
+
+}
+else if(my_other_bool) {
+
+}
+else {
+
+}
+```
+
+- Variable names follow those in the C++ standard, basically snake_case.
+- Maximum column length is 125
+- Trailing return type will always be in the same line. Even if it goes off the column length. e.g.
+`auto f() -> decltype(/* my long expression */) {`
+- Since this is a header-only library, all free functions must be marked `inline`.
+- Use braces in optional contexts like `if`, `for`, `else`, `while`, etc. e.g.
+
+```cpp
+if(x > 12) {
+    return x * 2;
+}
+```
+
+- Use `typename` instead of `class` for template parameters. e.g. `template<typename T>`.
+
+If you don't meet all of these style guidelines, don't fret. I'll probably fix it. But please
+do make an effort to actually meet them. Otherwise I'm more likely to reject the pull request.

README.md

@@ -11,6 +11,10 @@ Lua errors are thrown as exceptions instead. This allows you to handle the error
 It should be noted that the library itself depends on `lua.hpp` to be found by your compiler. It uses angle brackets, e.g.
 `#include <lua.hpp>`. 
 
+## Contributing
+
+If you want to contribute, please check CONTRIBUTING.md for details. Thank you!
+
 ## Example
 
 Here's an example on how to load a basic configuration struct with a Lua script.