Add beginner walkthrough documentation

docs/dev/beginner-walkthrough.md

@@ -52,7 +52,7 @@ cargo build
 This will take about **2 minutes** to download dependencies and **12 minutes** to build in debug mode. At this point, you only built the substrate client, a kind of "shell" in which lies the runtime. You can build the runtime and run a local blockchain with:
 
 ```bash
-cargo run -- --dev --tmp
+cargo run -- --dev --tmp # here, --dev means --chain=gdev which selects the gdev runtime
 ```
 
 Which should take about **1 minute**. When you see the logs, the blockchain is running and you can connect to it with polkadotjs app: [https://polkadot.js.org/apps/?rpc=ws://127.0.0.1:9944](https://polkadot.js.org/apps/?rpc=ws%3A%2F%2F127.0.0.1%3A9944). You should see blocks being added every 6 seconds. You can use Alice, Bob, etc test accounts to submit extrinsics.
@@ -64,13 +64,13 @@ When using Duniter commands, you will benefit a lot from commands autocompletion
 ```bash
 # create local dir to store completion script
 mkdir -p ~/.local/share/duniter
-# build in release mode and export the bash completion file
-cargo run --release -- completion --generator bash > ~/.local/share/duniter/completion.bash
+# export the bash completion file
+cargo run -- completion --generator bash > ~/.local/share/duniter/completion.bash
 # add the following line to your ~/.bashrc to automatically load completion on startup
 [[ -f $HOME/.local/share/duniter/completion.bash ]] && source $HOME/.local/share/duniter/completion.bash
 ```
 
-Building in release mode for the first time is very long and can take up to **20 minutes**. You will then benefit from completion using `<Tab>` key and `*`.
+You will then benefit from completion using `<Tab>` key and `*`.
 
 ## End-to-end tests using cucumber