Refactor and improve documentation, add examples

docs/recipes/git-clone.md

@@ -0,0 +1,32 @@
+# Recipe: `git clone` / `git fetch`
+
+Goal: allow fetching code from a limited set of hosts.
+
+## HTTPS clone (GitHub example)
+
+```json
+{
+  "network": {
+    "allowedDomains": ["github.com", "api.github.com", "codeload.github.com"]
+  },
+  "filesystem": {
+    "allowWrite": ["."]
+  }
+}
+```
+
+Run:
+
+```bash
+fence --settings ./fence.json git clone https://github.com/OWNER/REPO.git
+```
+
+## SSH clone
+
+SSH traffic may go through SOCKS5 (`ALL_PROXY`) depending on your git/ssh configuration.
+
+If it fails, use monitor/debug mode to see what was blocked:
+
+```bash
+fence -m --settings ./fence.json git clone git@github.com:OWNER/REPO.git
+```