Fix some spellings

Author: ehuss

guide/src/format/configuration/preprocessors.md

@@ -35,7 +35,7 @@ For example, if you have a preprocessor called `mdbook-example`, then you can in
 With this table, mdBook will execute the `mdbook-example` preprocessor.
 
 This table can include additional key-value pairs that are specific to the preprocessor.
-For example, if our example prepocessor needed some extra configuration options:
+For example, if our example preprocessor needed some extra configuration options:
 
 ```toml
 [preprocessor.example]

guide/src/format/markdown.md

@@ -223,7 +223,7 @@ To enable it, see the [`output.html.curly-quotes`] config option.
 
 ### Heading attributes
 
-Headings can have a custom HTML ID and classes. This lets you maintain the same ID even if you change the heading's text, it also let's you add multiple classes in the heading.
+Headings can have a custom HTML ID and classes. This lets you maintain the same ID even if you change the heading's text, it also lets you add multiple classes in the heading.
 
 Example:
 ```md