add quoting to split_part (#528)

* add quoting to split_part

* update docs for split_part

* typo

* corrected readme syntax

* revert and update to just documentation

* add new line

* Update README.md

* Update README.md

* Update README.md

Co-authored-by: Joel Labes <joel.labes@dbtlabs.com>

README.md

@@ -965,9 +965,16 @@ This macro calculates the difference between two dates.
 #### split_part ([source](macros/cross_db_utils/split_part.sql))
 This macro splits a string of text using the supplied delimiter and returns the supplied part number (1-indexed).
 
+**Args**:
+- `string_text` (required): Text to be split into parts. 
+- `delimiter_text` (required): Text representing the delimiter to split by.
+- `part_number` (required): Requested part of the split (1-based). If the value is negative, the parts are counted backward from the end of the string.
+
 **Usage:**
+When referencing a column, use one pair of quotes. When referencing a string, use single quotes enclosed in double quotes.
 ```
-{{ dbt_utils.split_part(string_text='1,2,3', delimiter_text=',', part_number=1) }}
+{{ dbt_utils.split_part(string_text='column_to_split', delimiter_text='delimiter_column', part_number=1) }}
+{{ dbt_utils.split_part(string_text="'1|2|3'", delimiter_text="'|'", part_number=1) }}
 ```
 
 #### date_trunc ([source](macros/cross_db_utils/date_trunc.sql))