Typo fix in class name. (#662)

Summary:
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Typo fix in class name. The correct class name here is `SectionContext` and not SectionContent.

## Changelog

SectionContent -> SectionContext
Pull Request resolved: #662

Test Plan: Verified in PlaygroundActivity and buck build.

Reviewed By: arpitratan

Differential Revision: D21649885

Pulled By: topwu

fbshipit-source-id: 6f2d11174c03c05b0b2638f82d2958dc3b5fe014

docs/_docs/sections-building-blocks.md

@@ -114,7 +114,7 @@ The Sections hierarchy becomes a “data source” for the `RecyclerCollectionCo
 
 ```java
 final Component listComponent = RecyclerCollectionComponent.create(c)
-    .section(MyGroupSection.create(new SectionContent(c))
+    .section(MyGroupSection.create(new SectionContext(c))
         .dataModel(...)
         .build())
     .build();