add CONTRIBUTING.md file

CONTRIBUTING.md

@@ -0,0 +1,17 @@
+Do you want to...
+
+* **Ask for help using SMAPI?**  
+  Please post a message in the [SMAPI support thread](http://community.playstarbound.com/threads/108375),
+  don't create a GitHub issue.
+  
+* **Report a bug?**  
+  Please post a message in the [SMAPI support thread](http://community.playstarbound.com/threads/108375)
+  instead, unless you're sure it's a bug in SMAPI itself.
+
+* **Submit a pull request?**  
+  Pull requests are welcome! If you're submitting a new feature, it's best to discuss first to make
+  sure it'll be accepted. Feel free to come chat in [#modding on Discord](https://discord.gg/kH55QXP)
+  or post in the [SMAPI support thread](http://community.playstarbound.com/threads/108375).
+  
+  Documenting your code and using the same formatting conventions is appreciated, but don't worry too
+  much about it. We'll fix up the code after we accept the pull request if needed.

src/StardewModdingAPI.sln

@@ -1,7 +1,7 @@
 
 Microsoft Visual Studio Solution File, Format Version 12.00
 # Visual Studio 15
-VisualStudioVersion = 15.0.26430.4
+VisualStudioVersion = 15.0.26430.14
 MinimumVisualStudioVersion = 10.0.40219.1
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "TrainerMod", "TrainerMod\TrainerMod.csproj", "{28480467-1A48-46A7-99F8-236D95225359}"
 EndProject
@@ -12,6 +12,7 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "metadata", "metadata", "{86
 		.editorconfig = .editorconfig
 		..\.gitattributes = ..\.gitattributes
 		..\.gitignore = ..\.gitignore
+		..\CONTRIBUTING.md = ..\CONTRIBUTING.md
 		crossplatform.targets = crossplatform.targets
 		GlobalAssemblyInfo.cs = GlobalAssemblyInfo.cs
 		..\LICENSE = ..\LICENSE