docs: Add index page

Author: hyperupcall

docs/index.md

@@ -0,0 +1,7 @@
+# bash-algo
+
+There are three parts:
+
+- FOr basen encoding/decoding, see [Algo](./algo.md)
+- For PEM encoding/decoding, see [PEM](./pem.md)
+- For url encoding/decoding, see [URI](./uri.md)