Added example of using bash completion (#86)

Added example using bash completion.

Example clones into `~/.kubectx` for people who don't want to make modifications outside of `$HOME`.

README.md

@@ -114,7 +114,20 @@ them to any POSIX environment that has Bash installed.
     Note that the leading underscore seems to be a convention.  
     If not using oh-my-zsh, you could link to `/usr/share/zsh/functions/Completion` (might require sudo), depending on the `$fpath` of your zsh installation.  
     In case of error, calling `compaudit` might help.
-  - For bash/fish: Figure out how to install completion scripts and please document here
+  - For bash:
+    ```bash
+    git clone https://github.com/ahmetb/kubectx.git ~/.kubectx
+    COMPDIR=$(pkg-config --variable=completionsdir bash-completion)
+    ln -sf ~/.kubectx/completion/kubens.bash $COMPDIR/kubens
+    ln -sf ~/.kubectx/completion/kubectx.bash $COMPDIR/kubectx
+    cat << FOE >> ~/.bashrc
+    
+    
+    #kubectx and kubens
+    export PATH=~/.kubectx:\$PATH
+    FOE
+    ```
+  - For fish: Figure out how to install completion scripts and please document here
   
 Example installation steps: