add doc for the previous bash modularization

.bashrc

@@ -4,6 +4,10 @@
 
 #set -o vi
 
+#URL with an explanation of .bashrc, .bash_profile, etc. 
+#(rationale of my modularization):
+#https://www.baeldung.com/linux/bashrc-vs-bash-profile-vs-profile
+
 # If running interactively, then:
 if [ "$PS1" ]; then
     # don't put duplicate lines in the history. See bash(1) for more options