How to add bootstrap to share point master site ?

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If you are planning to apply Boostrap for all the pages within your SharePoint site

Check which master page you are using
Open SPD >> Master Pages
Edit the currently use master page(s) (You may have two in use: one for the publishing side and one for the system side)
Located the tag and within it, add the reference to boostrap (rather it is stored locally or using a CDN)
Repeat the steps to reference the following reset css, which will avoid conflict between the default CSS provided by SharePoint and Boostrap
Add the