added -h output to readme

README.md

@@ -0,0 +1,27 @@
+# snek
+
+## Usage
+
+```bash
+$ ./snek -h
+```
+```
+usage: snek [-h] [--root ROOT] [--exe EXE] {envs,root,exe,info,fork,bless} ...
+
+🐍
+
+optional arguments:
+  -h, --help            show this help message and exit
+  --root ROOT           conda root folder / prefix (read from the current env, if not given)
+  --exe EXE             conda or mamba executable (read from the current env, if not given)
+
+commands:
+  {envs,root,exe,info,fork,bless}
+    envs                print existing envs
+    root                print root
+    exe                 print exe
+    info                print info
+    fork                fork a conda env
+    bless               bless a conda env
+```
+