Improve docs for project map usage

USAGE.md

@@ -116,7 +116,7 @@ some/submodule/name = new project name
 
 ### Project Map Section
 
-A key value pair list separated by new line. Use when a project should be renamed to another when sent to the API.
+A key value pair list separated by new line. Use when a project should be renamed to another when sent to the API. The order of the project map is important, the first match is used.
 
 ```ini
 [projectmap]
@@ -126,7 +126,7 @@ projects/foo = new project name
 
 ### Project Api Key Section
 
-A key value pair list separated by new line. Use when a project should be sent using another api key other than the default on `settings.api_key`.
+A key value pair list separated by new line. Use when a project should be sent using another api key other than the default on `settings.api_key`. The order of the project api key is important, the first match is used.
 
 ```ini
 [project_api_key]
@@ -148,7 +148,7 @@ However, if an api key exists in your `~/.wakatime.cfg` file then it takes prece
 
 ### Git Submodule Project Map Section
 
-A key value pair list separated by new line. Use when a submodule project should be renamed to another when sent to the API.
+A key value pair list separated by new line. Use when a submodule project should be renamed to another when sent to the API. The order of the git submodule project map is important, the first match is used.
 
 ```ini
 [git_submodule_projectmap]