doc/developer_guide: update doc about installing teuthology

There are 2 more ways to install teuthology. Approach with boostrap
script is easier and more convenient while other approach is more
elaborate but manual, document both of them. Don't delete the currently
documented approach because it lets users install teuthology
conveniently in a custom virtual environment. So, keep all three.

Signed-off-by: Rishabh Dave <[email protected]>

Author: rishabh-d-dave

doc/dev/developer_guide/running-tests-locally.rst

@@ -52,12 +52,35 @@ Running your first test
 The Python tests in Ceph repository can be executed on your local machine
 using `vstart_runner.py`_. To do that, you'd need `teuthology`_ installed::
 
+    $ git clone https://github.com/ceph/teuthology
+    $ cd teuthology
+    $ ./bootstrap install
+
+This will create a virtual environment named ``virtualenv`` in root of the
+teuthology repository and install teuthology in it.
+
+You can also install teuthology via ``pip`` if you would like to install it
+in a custom virtual environment with clone `teuthology`_ repository using
+``git``::
+
     $ virtualenv --python=python3 venv
     $ source venv/bin/activate
     $ pip install 'setuptools >= 12'
     $ pip install teuthology[test]@git+https://github.com/ceph/teuthology
     $ deactivate
 
+If for some unforeseen reason above approaches do no work (maybe boostrap
+script doesn't work due to a bug or you can't download tethology at the
+moment) teuthology can be installed manually manually from copy of
+teuthology repo already present on your machine::
+
+    $ cd teuthology
+    $ virtualenv -p python3 venv
+    $ source venv/bin/activate
+    $ pip install -r requirements.txt
+    $ pip install .
+    $ deactivate
+
 The above steps installs teuthology in a virtual environment. Before running
 a test locally, build Ceph successfully from the source (refer
 :doc:`/install/build-ceph`) and do::