Add behavior spec to create project_dir

README.md

@@ -14,6 +14,14 @@ If the project exists in your project directory, it will spawn a subshell in tha
 
 When invoked as specified in usage (with any number of valid flags plus exactly one non-flag argument referred to here as `$arg1`), `proj` will do the following:
 
+* Check for the existence of `project_dir`
+
+  * If `project_dir` is a directory or symbolic link, proceed
+
+  * If `project_dir` is any other type of file, panic
+
+  * If `project_dir` does not exist, create it
+
 * `cd` to `project_dir` (normally `~/Projects`)
 
 * Check for the existence of `$arg1`