fix: Correct documentation text issues

[savvar9991]

1.Fixed spelling error in the word "support":

-### How to make your plugin suport string internationalization?
+### How to make your plugin support string internationalization?

Explanation: The word "suport" was missing the letter "p". The correct spelling is "support".

2. Fixed grammatical error in contraction:

-its better to provide a "defaultMessage"
+it's better to provide a "defaultMessage"

Explanation: "its" is a possessive pronoun, but in this context, we need the contraction of "it is", which is written as "it's".

[netlify]

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