Add usage instructions slide to presentation

pages/usage-slide.md

@@ -0,0 +1,51 @@
+---
+level: 2
+---
+
+# USAGE
+
+`infctl` has a single, compulsory parameter `[-f|--deployment-file]` and an optional environment variable `LOG_FORMAT` which may be ["none"|"basic"|""]
+
+there must be a valid `deployment-file` 
+
+`LOG_FORMAT` is used to switch structured log to be off, "none", 2 field with "basic" or JSON ( the default )
+
+
+
+````md magic-move {lines: true}
+```bash 
+export LOG_FORMAT=none 
+infctl 
+
+no config specified with --deployment-file=<path_to_config_file>
+```
+
+```bash 
+export LOG_FORMAT=none 
+infctl -f pipelines/dev/vagrant-k3s.json
+
+🔄 Running step: Create Vagrant nodes
+🐞 Running command: ./scripts/install_vagrant_nodes.sh
+...
+```
+
+```bash
+export LOG_FORMAT="basic"
+infctl -f pipelines/dev/vagrant-k3s.json
+
+level=INFO msg="Project name already exists: hdshd\n"
+level=INFO msg="🔄 Running step: Create Vagrant nodes"
+...
+```
+
+```bash
+export LOG_FORMAT=""
+infctl -f pipelines/dev/vagrant-k3s.json
+
+{"time":"2025-08-16T18:28:00.412416282+01:00","level":"INFO","msg":"Project name already exists: hdshd\n"}
+{"time":"2025-08-16T18:28:00.412511255+01:00","level":"INFO","msg":"🔄 Running step: Create Vagrant nodes"}
+...
+```
+
+
+````

slides.md

@@ -88,6 +88,11 @@ transition: fade-out
 src: ./pages/plugins-slide.md
 ---
 
+---
+transition: fade-out
+src: ./pages/usage-slide.md
+---
+
 ---
 transition: fade-out
 src: ./pages/infctl-summary.md