Update run.bat (#3783)

Co-authored-by: Richard Beales <rich@richbeales.net>

run.bat

@@ -1,8 +1,24 @@
 @echo off
-python scripts/check_requirements.py requirements.txt
+setlocal enabledelayedexpansion
+
+:FindPythonCommand
+for %%A in (python python3) do (
+    where /Q %%A
+    if !errorlevel! EQU 0 (
+        set "PYTHON_CMD=%%A"
+        goto :Found
+    )
+)
+
+echo Python not found. Please install Python.
+pause
+exit /B 1
+
+:Found
+%PYTHON_CMD% scripts/check_requirements.py requirements.txt
 if errorlevel 1 (
     echo Installing missing packages...
-    pip install -r requirements.txt
+    %PYTHON_CMD% -m pip install -r requirements.txt
 )
-python -m autogpt %*
+%PYTHON_CMD% -m autogpt %*
 pause