WIP: Asciidoc (#407)

* Rename readme

* Add some Asciidoc demo

* Remove extra lines

substrate/polkadot/cli/doc/shell-completion.adoc

@@ -0,0 +1,41 @@
+
+== Shell completion
+
+The Polkadot cli command supports shell auto-completion. For this to work, you will need to run the completion script matching you build and system.
+
+Assuming you built a release version using `cargo build --release` and use `bash` run the following:
+
+[source, shell]
+source target/release/completion-scripts/polkadot.bash
+
+You can find completion scripts for:
+- bash
+- fish
+- zsh
+- elvish
+- powershell
+
+To make this change persistent, you can proceed as follow:
+
+.First install
+
+[source, shell]
+----
+COMPL_DIR=$HOME/.completion
+mkdir -p $COMPL_DIR
+cp -f target/release/completion-scripts/polkadot.bash $COMPL_DIR/
+echo "source $COMPL_DIR/polkadot.bash" >> $HOME/.bash_profile
+source $HOME/.bash_profile
+----
+
+.Update
+
+When you build a new version of Polkadot, the following will ensure you auto-completion script matches the current binary:
+
+[source, shell]
+----
+COMPL_DIR=$HOME/.completion
+mkdir -p $COMPL_DIR
+cp -f target/release/completion-scripts/polkadot.bash $COMPL_DIR/
+source $HOME/.bash_profile
+----