Fix improper idiom usage (#5883)

* Fix casing for consistency

There's 5 instances in this document in which the casing of a file name
begins with lower case, which makes it inconsisnent both with the page
and the entire tutorial.

* Fix improper idiom usage

The phrase "most of the times" is incorrect and would only make sense
in the context of a larger sentence. The phrase is actually "most of the
time" and is used in place of "usually".

src/content/learn/writing-markup-with-jsx.md

@@ -126,7 +126,7 @@ This is because JSX is stricter and has a few more rules than HTML! If you read
 
 <Note>
 
-Most of the times, React's on-screen error messages will help you find where the problem is. Give them a read if you get stuck!
+Most of the time, React's on-screen error messages will help you find where the problem is. Give them a read if you get stuck!
 
 </Note>