[docs] add more sections

docs/in-depth/configuration-variables.md

@@ -0,0 +1,40 @@
+# Configuration variables
+
+The `screeps.json` file is a JSON configuration file separated into multiple environments. We've given you three primary environments by default.
+
+```json
+{
+  // Used for deploying to the main world
+  "main": {
+    "email": "you@provider.tld",
+    "password": "Password",
+    "protocol": "https",
+    "hostname": "screeps.com",
+    "port": 443,
+    "path": "/",
+    "branch": "main"
+  },
+  // Used for deploying to Simulation mode
+  "sim": {
+    "email": "you@provider.tld",
+    "password": "Password",
+    "protocol": "https",
+    "hostname": "screeps.com",
+    "port": 443,
+    "path": "/",
+    "branch": "sim"
+  },
+  // Used for deploying to a private server
+  "pserver": {
+    "email": "username",
+    "password": "Password",
+    "protocol": "http",
+    "hostname": "1.2.3.4",
+    "port": 21025,
+    "path": "/",
+    "branch": "main"
+  }
+}
+```
+
+[TODO: running environments]