You can use the Blender Typewriter Addon:
copy and paste the code into the Text Editor, then press alt + p to run the script.
Select your text object and you'll find a new panel into the Font Propery Panel:
Type the text in "source_text" field (NELLY).
Go to frame 0 and insert a keyframe for the character_count = 0 (mouse over the field and press i)
Go to frame 75, change character_count to 5 (text length) and press i
EDIT: Animation Nodes Addon
If you need more control (such as animating letters size, rotation...), you could use the Animation Nodes Addon.
Here you can find a video showing an advanced text manipulation: