How to reproduce:
1. Create a new 3D project.
2. Go to "Window->Package Manager->All" and import "Render-pipelines.lightweight" package.
3. After the package is imported, go to "Edit->Project Settings->Graphics".
4. Check "Scriptable Render Pipeline Settings". You can also search for "LWRP" asset in the project's folder.

Expected result: "Scriptable Render Pipeline Settings" will have a Lightweight Pipeline Asset attached to it. There will be at least one LWRP asset in the project's folder.
Actual result: "Scriptable Render Pipeline Settings" is set to "None" and cannot find any Render Pipeline Asset. There is no LWRP asset in the project's folder.

Reproducible with - 2018.1.0b7, 2018.1.0f1, 2018.2.0b1

Notes:
- "Render-Pipelines.lightweight" package could be found only in package managers from 2018.1.0b7 and newer versions of Unity.
- Missing Lightweight Pipeline Asset prevents users from using Shader Graph - any created shader will have a pink colour.

Fixed (by design):
Lightweight Pipeline Asset needs user settings and such things cannot be stored in a package. When you import LWRP through Package Manager, you also need to create Lightweight Pipeline Asset and attach it to Edit->Project Settings->Graphics->Scriptable Render Pipeline Settings yourself.