feat: custom python command

See #14

README.md

@@ -26,7 +26,12 @@ require("neotest").setup({
         -- Runner to use. Will use pytest if available by default.
         -- Can be a function to return dynamic value.
         runner = "pytest",
-
+        -- Custom python path for the runner.
+        -- Can be a string or a list of strings.
+        -- Can also be a function to return dynamic value.
+        -- If not provided, the path will be inferred by checking for 
+        -- virtual envs in the local directory and for Pipenev/Poetry configs
+        python = ".venv/bin/python"
         -- Returns if a given file path is a test file.
         -- NB: This function is called a lot so don't perform any heavy tasks within it.
         is_test_file = function(file_path)