docs(add, rename): 4 sets. session > user, regular > global

Author: olets

README.md

@@ -202,6 +202,8 @@ abbr a="b|c" # allowed
 
 User-scope abbreviations can also be manually to the user abbreviations file. See the Storage documentation, below.
 
+The session regular, session global, user regular, and user global abbreviation sets are independent. Order of precedence is "session command > user command > session global > user global".
+
 Use `--dry-run` to see what would result, without making any actual changes.
 
 #### Clear Sessions
@@ -414,6 +416,8 @@ Use the **--global** flag to rename a global abbreviation. Otherwise a command a
 % gm[Space] # expands to git checkout master
 ```
 
+Rename is session/user- and regular/global-specific. If you get a "no matching abbreviation" error, make sure you added the right flags.
+
 Use `--dry-run` to see what would result, without making any actual changes..
 
 Abbreviations can also be manually renamed in the `ZSH_USER_ABBREVIATIONS_PATH`.