Updated README.md

Just adding some links

Author: tedsecretsource

README.md

@@ -3,3 +3,8 @@
 Get DNS records in a CSV format from a file with a list of domains.
 
 `mx.sh --domains 'path/to/domain/file/with/one/domain/on/each/line' --record 'MX'`
+
+Sources of inspiration
+https://dev.to/thiht/shell-scripts-matter
+http://redsymbol.net/articles/unofficial-bash-strict-mode/
+https://www.gnu.org/software/bash/manual/html_node/Bash-Conditional-Expressions.html