Add fish-spec plugin README.

plugins/fish-spec/README.markdown

+# fish-spec
+> Unit testing as simple as fish.
+
+The following guide describes how to use the `fish-spec` plugin that is bundled with Oh-My-Fish.
+
+## Install
+Before you can use `fish-spec`, you need to install [Oh-My-Fish](https://github.com/bpinto/oh-my-fish).
+
+## Usage
+Just like any other plugin in Oh-My-Fish, you can start using `fish-spec` in two ways:
+
+1. Adding the plugin to the `$fish_plugins` global variable declared in your fish configuration file, usually in  `~/.config/fish/config.fish`.
+2. Directly importing the library into your fish file via [import](https://github.com/bpinto/oh-my-fish/blob/master/functions/import.fish).
+
+As of now, the most common use case is the second method, as you will probably want to test your own plugins or libraries.
+
+Inside your project's directory create a new `spec` folder (recommended) and add all your _spec_ files inside. _Spec_ files are regular fish files that must look like `*.spec.fish` and contain your tests.
+
+You can have multiple `spec.fish` files to organize your tests in a per module basis, or you can squash everything into a single file and use describe blocks to separate groups of tests.
+
+A `spec.file` usually looks like this:
+
+```fish
+import plugins/fish-spec
+import path/to/the-library # plugins/the-library
+
+# Use -d to enter a friendly description (optional)
+function describe_library -d "the grand library"
+
+  function before_all
+  # Optional. Runs only once before all the tests.
+  end
+
+  function after_all
+  # Optional. Runs only once after all the tests.
+  end
+
+  function before_each
+  # Optional. Runs once before each test.
+  end
+
+  function after_each
+  # Optional. Runs once after each test.
+  end
+
+  function it_does_this
+    # ...
+    expect $what_I_got --to-equal $what_I_wanted
+  end
+
+  function it_does_that
+    # ...
+    expect $a_list --to-contain-all $expected_items
+  end
+
+  # ...
+end
+
+# Run tests when this file is sourced.
+spec.run $argv
+```
+
+## API
+
+As of now, there is only one method you should be aware of, [expect](https://github.com/bpinto/oh-my-fish/blob/master/plugins/fish-spec/expect.fish):
+
+> Assert a list of expected values match an actual value/s.
+
+Under the hood, _expect_ checks an _actual_ value, usually a relevant result from your test unit, is equal to, not equal to, etc., to an _expected_ value, as determined by your test. Below are the list of conditions available to use with `expect`:
+
+* __--to-equal__             `<actual>` value equals `<expected>` value
+* __--to-not-equal__         `<actual>` value does not equals `<expected>` value
+* __--to-contain-all__       all `<actual>` values exist in `<expected>` list
+* __--to-not-contain-all__   all `<actual>` values does not exist in `<expected>` list
+* __--to-be-true__           exit status should be _truthy_
+* __--to-be-false__          exit status should be _falsy_
+
+## FAQ
+1. __How to use `fish-spec` without Oh-My-Fish?__
+`fish-spec` is still a work in progress and as it currently stands, it is only available bundled with Oh-My-Fish. As the library matures and grows, however, it is possible a future guide describing how to export `fish-spec` will be written.
+
+## Authors
++ [Bruno Pinto](https://github.com/bpinto)
++ [Jorge Bucaran](https://bucaran.me)
+
+## License
+[MIT](http://opensource.org/licenses/MIT)