Commands in section 'Install from GitHub' won't install grav

**Do you want to request a *feature* or report a *bug*?**
a *bug*

**What is the current behavior?**
Executing the commands listed in [Option 3: Install from GitHub](https://github.com/getgrav/grav-learn/blob/develop/pages/01.basics/03.installation/docs.md#option-3-install-from-github) won't install grav.

```bash
$ cd ~/webroot
$ git clone -b master https://github.com/getgrav/grav.git
```
This will clone grav into `~/webroot/grav` thus executing `composer install --no-dev -o` won't install anything (*Composer could not find a composer.json file in ~/webroot*).

To correctly install grav in subfolder `grav` the line `$ cd ~/webroot/grav` from step 3 (Install ... using the Grav CLI application bin/grav) should be moved to step 2 (Install vendor dependencies via composer) before running `composer install`.

**If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem**

Just run the commands as listed in the documentation.

**What is the expected behavior?**
Grav should be installed and running after executing the commands from the docs.

**Which versions of OS are affected by this issue? Did this work in previous versions?**
git version 2.1.4

Open pages/01.basics/03.installation/docs.md and review Option 3: Install from GitHub, especially the command order around cloning, changing into grav, and running Composer. Reproduce the documented commands, then update the steps so the commands run from the cloned grav directory and verify that Grav installs successfully.

Written by the indexing model from the issue text.