Make it easier to run src/top_evil_rs.py from git root

Currently, `src/top_evil_rs.py' script recursively scans current
directory for Rust sources and print statistics about them.

When run from git root, it also scans target/ directory, which is
useless.

This commit add cludge that checks if script is run from git root
directory, and `chdir' into `src/' before performing actions.

Unprincipled, but convenient.

src/top_evil_rs.py

@@ -6,6 +6,8 @@ import os
 import re
 
 if __name__ == "__main__":
+    if Path('src/top_evil_rs.py').exists():
+        os.chdir('src')
     filestats = []
     for fn in Path(".").glob("**/*.rs"):
         s = fn.read_text()