@emotion/cache readme: fix minor typos (#1410)

* Fix minor typos in @emotion/cache readme

- Add missing comma before non-restrictive 'which'
- Use gerunds consistently in 'Primary use cases' section
- Fix [comma splices](https://en.wikipedia.org/wiki/Comma_splice) in 'Options' section
- Correct the spelling of 'dynamically'
- Use proper form of possessive 'its'

* Update options formatting in @emotion/cache readme

Match the formatting of [babel-plugin-emotion readme](https://github.com/emotion-js/emotion/blob/master/packages/babel-plugin-emotion/README.md#sourcemap) by putting the type and default value on a separate line just below the option name.

(Also standardize capitalization of "Stylis" and avoid the somewhat awkward possessive "Stylis's" where possible.

packages/cache/README.md

@@ -2,7 +2,7 @@
 
 ### createCache
 
-`createCache` allows for low level customization of how styles get inserted by emotion. It's intended to be used with the [`<CacheProvider/>`](https://emotion.sh/docs/cache-provider) component to override the default cache which is created with sensible defaults for most applications.
+`createCache` allows for low level customization of how styles get inserted by emotion. It's intended to be used with the [`<CacheProvider/>`](https://emotion.sh/docs/cache-provider) component to override the default cache, which is created with sensible defaults for most applications.
 
 ```javascript
 import createCache from '@emotion/cache'
@@ -21,28 +21,38 @@ export const myCache = createCache({
 
 - Setting a [nonce](#nonce-string) on any `<style/>` tag emotion creates for security purposes
 
-- Use emotion with a developer defined `<style/>` tag
+- Using emotion with a developer defined `<style/>` tag
 
-- Using emotion with custom stylis plugins
+- Using emotion with custom Stylis plugins
 
 ## Options
 
-### nonce: string
+### `nonce`
+
+`string`
 
 A nonce that will be set on each style tag that emotion inserts for [Content Security Policies](https://developer.mozilla.org/en-US/docs/Web/HTTP/CSP).
 
-### stylisPlugins: Function | Array<Function>
+### `stylisPlugins`
+
+`Function` | `Array<Function>`
+
+A Stylis plugin or plugins that will be run by Stylis during preprocessing. [Read the Stylis docs to find out more](https://github.com/thysultan/stylis.js#plugins). This can be used for many purposes such as RTL.
+
+### `prefix`
+
+`boolean` | `Function`, defaults to `true`
 
-A Stylis plugin or plugins that will be run by stylis during preprocessing. [Read Stylis' docs to find out more](https://github.com/thysultan/stylis.js#plugins). This can for be used for many purposes such as RTL.
+Allows changing Stylis's vendor prefixing settings. It can be a boolean or a function to dynamically set which properties are prefixed. [More information can be found in the Stylis docs](https://github.com/thysultan/stylis.js#vendor-prefixing).
 
-### prefix: boolean | Function
+### `key`
 
-Allows changing Stylis' prefixing settings, this defaults to `true`. It can be a boolean or a function to dynamicly set which properties are prefixed. [More information can be found in Stylis' docs](https://github.com/thysultan/stylis.js#vendor-prefixing)
+`string`, defaults to `"css"`
 
-### key: string
+The prefix before class names. It will also be set as the value of the `data-emotion` attribute on the style tags that emotion inserts and it's used in the attribute name that marks style elements in `renderStylesToString` and `renderStylesToNodeStream`. This is **required if using multiple emotion caches in the same app**.
 
-The prefix before class names, this defaults to `css`. It will also be set as the value of the `data-emotion` attribute on the style tags that emotion inserts and it's used in the attribute name that marks style elements in `renderStylesToString` and `renderStylesToNodeStream`. This is **required if using multiple emotion caches in the same app**.
+### `container`
 
-### container: HTMLElement
+`HTMLElement`
 
-A DOM Node that emotion will insert all of it's style tags into, this is useful for inserting styles into iframes.
+A DOM node that emotion will insert all of its style tags into. This is useful for inserting styles into iframes.