Port README.md from main project

This patch basically takes the file currently under
Semantic-UI/src/README.md, modifies it a bit and include it here so that
there is a little bit more of an explanation on what the Semantic-UI-LESS
repository is about and it is supposed to be used.

README.md

@@ -0,0 +1,91 @@
+## Using LESS
+
+> LESS files do not contain vendor prefixes. If you are to use these files directly you must add them during your build step.
+
+Before using source files you will need to create a `theme.config` by renaming `theme.config.example`, and a site folder by renaming `_site/` to `site/`
+
+You can then import Semantic from your own LESS files:
+```less
+/* Import all components */
+@import 'src/semantic';
+```
+
+To import individual components you will have to create a scope for each import using `& {}`
+```less
+/* Import a specific component */
+& { @import 'src/definitions/elements/button'; }
+```
+
+### Config Files
+
+These files are generated automatically using install scripts, but must be manually renamed if you are using installing manually.
+
+filename | usage | Initial Name
+--- | --- | ---
+**theme.config** | config file that stores each element's current theme for LESS | theme.config.example
+**site/** | folder storing all your site's variables and css overrides for each UI component | _site/
+**semantic.json** | stores folder paths for build tools and current installed version for updates. Only necessary when using build tools | semantic.json.example
+
+
+### Workflow
+
+You will only need to use Semantic's build tools while refining your UI. When designing pages, you can rely on the compiled css packages in  `dist/`.
+
+When creating your UI you can try <a href="http://www.learnsemantic.com/themes/creating.html">downloading different themes</a>, adjusting your <a href="http://www.learnsemantic.com/developing/customizing.html#setting-global-variables">site-wide settings</a> (font-family, colors, etc) and tweaking components in your site's <a href="http://www.learnsemantic.com/developing/customizing.html#designing-for-the-long-now">component overrides</a>.
+
+Files in the  `examples/` folder of your project can be useful for testing out changes in your UI. For example, you might run  `gulp watch` download a new theme to  `src/site/themes/` then adjust your  `theme.config` file with the name of the new theme and refresh  `examples/kitchensink.html` to inspect changes in the theme.
+
+## Theming
+
+### Concepts
+
+#### Inheritance
+
+There are three levels of inheritance in Semantic
+* Default theme - Semantic UI's neutral default theme
+* Packaged theme - A specified packaged theme, like "amazon", or "material"
+* Site theme - A theme specific to your site
+
+#### Folder Structure
+
+* `definitions/` contains the `css` and `javascript` definitions for each component
+* `themes/` contains *pre-packaged themes* including Semantic's default theme
+* `site/` contains your current site's theme
+
+View the [Theming Guide](http://learnsemantic.com/themes/overview.html) for a more in-depth look
+
+## Customizing
+
+#### Basic Customization
+
+The best way to start customizing is to specify overriding variables in your site's `site.variables` file.
+
+This is a blank stub file that lets you specify variables that overriding variables.
+
+Some important values to customize:
+* Base font size
+* Named color hex codes
+* Header/Page Font-families
+* Primary and secondary colors
+* Grid column count
+
+To find out what variables are available to modify, you can inspect the variables in the default theme in `themes/default/`
+
+#### Advanced Configuration
+
+Each component has its own variable file, which can be used to modify any of the underlying variables for that component.
+
+For example `/site/elements/button.variables`.
+
+You may also specify your own custom LESS in `site/elements/button.overrides`. This file will have access to all underlying variables available for that component.
+
+#### Using Pre-Packaged Themes
+
+You can modify `theme.config` to use any prepackaged theme available in `src/themes/`.
+
+For example you can modify `theme.config` to use a `github` button theme by changing
+```less
+@button: 'github';
+```
+
+View the [Customization Guide](http://learnsemantic.com/developing/customizing.html) to learn more