Add documentation

README.md

@@ -1,5 +1,49 @@
 # @validatem/is-string
 
-Documentation for this module has not been written yet. By the time it reaches 1.0.0, it will have full documentation.
+*This validator is designed to be used with [Validatem](https://validatem.cryto.net/), the universal and composable validation library.*
 
-In the meantime, check out the `example.js` file in the repository for a usage demonstration.
+Validates that a given input is a string.
+
+Note that it __does not__ validate that the string is non-empty (ie. has a length above 0); for that, you should use [@validatem/is-non-empty-string](https://www.npmjs.com/package/@validatem/is-non-empty-string) instead.
+
+## License, donations, and other boilerplate
+
+Licensed under either the [WTFPL](http://www.wtfpl.net/txt/copying/) or [CC0](https://creativecommons.org/publicdomain/zero/1.0/), at your choice. In practice, that means it's more or less public domain, and you can do whatever you want with it. Giving credit is *not* required, but still very much appreciated! I'd love to [hear from you](mailto:admin@cryto.net) if this module was useful to you.
+
+Creating and maintaining open-source modules is a lot of work. A donation is also not required, but much appreciated! You can donate [here](http://cryto.net/~joepie91/donate.html).
+
+## Example
+
+A runnable version of this example is included in the repository, as `example.js`.
+
+```js
+"use strict";
+
+const { validateValue } = require("@validatem/core");
+const isString = require("@validatem/is-string");
+
+console.log(validateValue("hello world", [ isString ])); // hello world
+
+console.log(validateValue(42, [ isString ])); /*
+	AggregrateValidationError: One or more validation errors occurred:
+	- At (root): Must be a string
+*/
+
+```
+
+## API
+
+__If you are new to Validatem,__ please read the documentation on the [Validatem website](https://validatem.cryto.net/) first - it will explain how the general API works, and how you should use validator modules with it.
+
+### isString
+
+Not callable. Validates that the input is a string. When validation passes, it returns the original string as-is.
+
+Possible error codes:
+- __validatem.is-string:__ The input was not a string.
+
+## Changelog
+
+### 1.0.0 (August 8, 2020)
+
+Initial release.