Add info on editing documentation to CONTRIBUTING.md

CONTRIBUTING.md

@@ -23,6 +23,25 @@ Julia has a built-in [package manager](https://github.com/JuliaLang/METADATA.jl)
 
 For developers who need to wrap C libraries so that they can be called from Julia, the [Clang.jl](https://github.com/ihnorton/Clang.jl) package can help generate the wrappers automatically from the C header files.
 
+### Improving documentation
+
+*By contributing documentation to Julia, you are agreeing to release it under the [MIT License](https://github.com/JuliaLang/julia/tree/master/LICENSE.md).*
+
+Julia's documentation is stored in the `doc` directory, and like everything else can be modified using `git`. However, for small changes one can also use GitHub's web interface:
+
+- Navigate to https://github.com/JuliaLang/julia 
+- Click `doc` 
+- If you want to modify an entry in the help for Julia's standard library, click `stdlib`
+- Pick the file you want to edit (for example, `base.rst`)
+- Click "Edit" 
+- Click on the icon that looks like a fullscreen symbol ("Zen" mode) 
+- Search for the function you want to change
+- Make your changes 
+- Exit Zen mode 
+- Provide a title, and optionally a longer description of your change 
+- Submit your change
+
+
 ### Contributing to core functionality or base libraries
 
 *By contributing code to Julia, you are agreeing to release it under the [MIT License](https://github.com/JuliaLang/julia/tree/master/LICENSE.md).*