sed: reword last example and add it to the osx version too

pages/common/sed.md

@@ -22,6 +22,6 @@
 
 `sed -e 's/{{find}}/{{replace}}/' -e 's/{{find}}/{{replace}}/' {{filename}}`
 
-- Replace separator / by any other character not used in your string, e.g., #:
+- Replace separator / by any other character not used in the find or replace patterns, e.g., #:
 
 `sed 's#{{find}}#{{replace}}#' {{filename}}`

pages/osx/sed.md

@@ -21,3 +21,7 @@
 - Apply multiple find-replace expressions to a file:
 
 `sed -e 's/{{find}}/{{replace}}/' -e 's/{{find}}/{{replace}}/' {{filename}}`
+
+- Replace separator / by any other character not used in the find or replace patterns, e.g., #:
+
+`sed 's#{{find}}#{{replace}}#' {{filename}}`