(docs) fixed 404s and minor typos (#1639)

**Summary**
Fixed 404s (converted absolute links to relative links) and minor typos across several pages.

**Test plan**
Previewed locally

**A picture of a cute animal (not mandatory but encouraged)**
![pups](https://user-images.githubusercontent.com/31967674/44364132-353b6480-a494-11e8-9b01-ff7d32bfceda.jpg)

website/content/docs/widgets/index.md

@@ -4,7 +4,7 @@ weight: 30
 group: reference
 ---
 
-Widgets define the data type and interface for entry fields. Netlify CMS comes with several built-in widgets. Click the widget names in the sidebar to jump to specific widget details. We’re always adding new widgets, and you can also [create your own](https://www.netlifycms.org/docs/custom-widgets)!
+Widgets define the data type and interface for entry fields. Netlify CMS comes with several built-in widgets. Click the widget names in the sidebar to jump to specific widget details. We’re always adding new widgets, and you can also [create your own](../custom-widgets)!
 
 Widgets are specified as collection fields in the Netlify CMS `config.yml` file. Note that [YAML syntax](https://en.wikipedia.org/wiki/YAML#Basic_components) allows lists and objects to be written in block or inline style, and the code samples below include a mix of both.
 
@@ -17,7 +17,7 @@ The following options are available on all fields:
 
 - `required`: specify as `false` to make a field optional; defaults to `true`
 - `hint`: optionally add helper text directly below a widget. Useful for including instructions.
-- `pattern`: add field validation by specifying a list with a [regex pattern](https://regexr.com/) and an error message; more extensive validation can be achieved with [custom widgets](https://www.netlifycms.org/docs/custom-widgets/#advanced-field-validation)
+- `pattern`: add field validation by specifying a list with a [regex pattern](https://regexr.com/) and an error message; more extensive validation can be achieved with [custom widgets](../custom-widgets/#advanced-field-validation)
   - **Example:**
         ```yaml
         - label: "Title"

website/content/docs/widgets/markdown.md

@@ -5,7 +5,7 @@ target: markdown
 
 The markdown widget provides a full fledged text editor - which is based on [slate](https://github.com/ianstormtaylor/slate) - that allows users to format text with features such as headings and blockquotes. Users are also allowed to write in markdown by simply flipping a switch.
 
-*Please note:* in case you want to use your markdown editor to fill a markdown's file content after the frontmatter, you'll have name the field as `body` so then the CMS can recognize it and save the file accordingly.
+*Please note:* in case you want to use your markdown editor to fill a markdown's file content after the frontmatter, you'll have name the field as `body` so that the CMS can recognize it and save the file accordingly.
 
 - **Name:** `markdown`
 - **UI:** full text editor