replace trailing whitespace with blackslash in README.md

As an alternative to the markdown trailing whitespace as a line
break, we use a trailing blackslash as a markdown line break.

2005/mikeash/README.md

@@ -1,8 +1,8 @@
 # Best use of parenthesis
 
-Michael Ash  
-US  
-mike@mikeash.com  
+Michael Ash\
+US\
+mike@mikeash.com\
 <https://mikeash.com>
 
 ## To build: