Update Doc fix #480 #477

CONTRIBUTING.md

@@ -1,3 +1,5 @@
+## Contributing to `rio`
+
 Contributions to **rio** are welcome from anyone and are best sent as pull requests on [the GitHub repository](https://github.com/gesistsa/rio/). This page provides some instructions to potential contributors about how to add to the package.
 
  1. Contributions can be submitted as [a pull request](https://help.github.com/articles/creating-a-pull-request/) on GitHub by forking or cloning the [repo](https://github.com/gesistsa/rio/), making changes and submitting the pull request.

vignettes/philosophy.Rmd

@@ -41,4 +41,4 @@ The core advantage of **rio** is that it makes assumptions that the user is prob
 
       In addition, two functions (added in v0.5.5) provide easy ways to create character and factor variables from these "labels" attributes. `characterize()` converts a single variable or all variables in a data frame that have "labels" attributes into character vectors based on the mapping of values to value labels. `factorize()` does the same but returns factor variables. This can be especially helpful for converting these rich file formats into open formats (e.g., `export(characterize(import("file.dta")), "file.csv")`.
 
- 8. **rio** imports and exports files based on an internal S3 class infrastructure. This means that other packages can contain extensions to **rio** by registering S3 methods. These methods should take the form `.import.rio_X()` and `.export.rio_X()`, where `X` is the file extension of a file type. An example is provided in the [rio.db package](https://github.com/leeper/rio.db).
+ 8. **rio** imports and exports files based on an internal S3 class infrastructure. This means that other packages can contain extensions to **rio** by registering S3 methods. These methods should take the form `.import.rio_X()` and `.export.rio_X()`, where `X` is the file extension of a file type. Please refer to the "Extending rio" vignette (`vignette(topic = "extension", package = "rio")`).