Add usage docs and move polygen app

.polygen.example.yml

@@ -0,0 +1,9 @@
+# List of collections for which you want to generate code.
+collection:
+  - "Collection"
+  - "Namespace/Collection"
+
+language:
+  go:
+    package: "package_name"
+    directory: "directory/to/save"

README.md

@@ -7,7 +7,32 @@
 ## Install PolyGen
 
 ```bash
-go install github.com/durudex/polygen/cmd@latest
+go install github.com/durudex/polygen/cmd/polygen@latest
+```
+
+## Usage
+
+1) To start working with PolyGen, you need to create a configuration according
+to which the code will be generated.
+
+```yml
+collection:
+  - "Collection"
+
+language:
+  go:
+    package: "generated"
+    directory: "generated"
+```
+
+> You can find the complete configuration in the 
+> [.polygen.example.yml](.polygen.example.yml) file.
+
+2) Now you need to run PolyGen with the `--config` or `-c` flag and specify the
+path to your configuration file.
+
+```bash
+polygen --config .polygen.yml
 ```
 
 ## ⚠️ License