How to migrate from Py2 to Py3 (#1355)

* How to migrate from Py2 to Py3

The commands done to migrate Ubuntu from Py2 to Py3.

* Update Migrating-to-Python3

docs/installation/Migrating-to-Python3

@@ -0,0 +1,27 @@
+# Migration
+Remove Python 2 packages
+```no-highlight
+# apt-get remove --purge -y python-dev python-pip
+```
+
+Install Python 3 packages
+```no-highlight
+# apt-get install -y python3 python3-dev python3-pip
+```
+
+Install Python Packages
+```no-highlight
+# cd /opt/netbox
+# pip3 install -r requirements.txt
+```
+
+Gunicorn Update
+```
+# pip uninstall gunicorn
+# pip3 install gunicorn
+```
+
+Re-install LDAP Module (Optional if using LDAP for auth)
+```
+sudo pip3 install django-auth-ldap
+```