[AppBar] Add Theming Section to README.md
* Update README.md
Added Theming Documentation to AppBar.
* Update README.md
* Update README.md
Made some minor changes.
* Update README.md
minor fix
* Update README.md
applySemanticColorScheme
MODIFY
components/AppBar/README.md
components/AppBar/README.md
@@ -249,3 +249,59 @@ recommendation for building interactive background views is the following:
[Usage](../FlexibleHeader/#usage) docs.
3. Add your views to this flexible header instance.
4. Create a Navigation Bar if you need one. Treat it like any other custom view.
+
+### Theming
+
+You can theme an AppBar with your app's color scheme and typography scheme using the ColorThemer and TypographyThemer extensions.
+
+You must first add the Themer extensions to your project:
+
+``` bash
+pod 'MaterialComponents/AppBar+Extensions/ColorThemer'
+pod 'MaterialComponents/AppBar+Extensions/TypographyThemer'
+```
+
+You can then import the theming APIs:
+
+<!--<div class="material-code-render" markdown="1">-->
+#### Swift
+``` swift
+import MaterialComponents.MaterialAppBar_ColorThemer
+import MaterialComponents.MaterialAppBar_TypographyThemer
+```
+
+#### Objective-C
+
+``` objc
+#import "MaterialAppBar+ColorThemer.h"
+#import "MaterialAppBar+TypographyThemer.h"
+```
+<!--</div>-->
+
+MDCAppBarColorThemer allows you to theme an app bar with your app's color scheme.
+
+MDCAppBarTypographyThemer allows you to theme an app bar with your app's typography scheme.
+
+<!--<div class="material-code-render" markdown="1">-->
+#### Swift
+``` swift
+let colorScheme = MDCSemanticColorScheme()
+let typographyScheme = MDCTypographyScheme()
+
+let appBar = MDCAppBar()
+MDCAppBarColorThemer.applySemanticColorScheme(colorScheme, to: appBar)
+MDCAppBarTypographyThemer.apply(typographyScheme, to: appBar)
+```
+
+#### Objective-C
+
+``` objc
+id<MDCColorScheming> colorScheme = [[MDCSemanticColorScheme alloc] init];
+id<MDCTypographyScheming> typographyScheme = [[MDCTypographyScheme alloc] init];
+
+MDCAppBar *appBar = [[MDCAppBar alloc] init];
+[MDCAppBarColorThemer applySemanticColorScheme:colorScheme toAppBar:appBar];
+[MDCAppBarTypographyThemer applyTypographyScheme:typographyScheme toAppBar:appBar];
+
+```
+<!--</div>-->

[AppBar] Add Theming Section to README.md (#3516)

* Update README.md

Added Theming Documentation to AppBar.

* Update README.md

* Update README.md

Made some minor changes.

* Update README.md

minor fix

* Update README.md

applySemanticColorScheme

https://github.com/material-components/material-components-ios/pull/3516