Fix minor typos in string manipulation section (#2123)

Co-authored-by: Darren Schroeder <343840+fdncred@users.noreply.github.com>

Author: c-git

book/working_with_strings.md

@@ -180,7 +180,7 @@ You can also use the [`run-external`](/commands/docs/run-external.md) command fo
 
 ## Appending and Prepending to strings
 
-There are various ways to pre, or append strings. If you want to add something to the beginning of each string closures are a good option:
+There are various ways to prepend, or append strings. If you want to add something to the beginning of each string, closures are a good option:
 
 ```nu
 ['foo', 'bar'] | each {|s| '~/' ++ $s} # ~/foo, ~/bar
@@ -194,7 +194,7 @@ You can also use a regex to replace the beginning or end of a string:
 ['foo', 'bar'] | str replace -r '$' '~/'# foo~/, bar~/
 ```
 
-If you want to get one string out of the end then `str join` is your friend:
+If you want to combine a list into a string, then `str join` is your friend:
 
 ```nu
 "hello" | append "world!" | str join " " # hello world!

book/working_with_tables.md

@@ -195,7 +195,7 @@ $first | append $second
 # => ───┴───┴───
 ```
 
-If the column names are not identical then additionally columns and values will be created as necessary:
+If the column names are not identical then additional columns and values will be created as necessary:
 
 ```nu
 let first = [[a b]; [1 2]]