Line.md

+Line original implementation. Provides an easy interface to manipulate, save and restore, line-like values from the database. Works very similar to the `ActiveRecord::Point`, but for the values that compose a line (`a`, `b`, and `c`). [PostgreSQL Docs](https://www.postgresql.org/docs/9.6/datatype-geometric.html#DATATYPE-LINE)
+
+The biggest difference between this and a [`segment`](https://github.com/crashtech/torque-postgresql/wiki/Segment) is that its composition is based on the [`A, B, C` form](https://en.wikipedia.org/wiki/Line_(geometry)#In_Euclidean_geometry) `0 = Ax + By + C`.
+
+# How it works
+
+### Migration
+
+Just set the type of the column as `line` when creating a table.
+```ruby
+create_table "Hit" do |t|
+  t.string "source", null: false
+  t.line   "trajectory"
+end
+```
+
+### Using it
+
+The column is automatically identified and its value turned into what is defined in [`geometry.line_class`](https://github.com/crashtech/torque-postgresql/wiki/Configuring#geometry.line_class) or into a `Torque::PostgreSQL::Line`. 
+
+This original implementation provides a couple of methods:
+```ruby
+hit = Hit.new
+hit.trajectory.a
+hit.trajectory.b
+hit.trajectory.c
+hit.trajectory.horizontal?
+hit.trajectory.cvertical?
+hit.trajectory.intercept      # Same as c
+```
+
+The value can be set in some different manners:
+
+```ruby
+hit.trajectory = '2,-5,4'
+hit.trajectory = '{2,-5,4}'
+hit.trajectory = [2,-5,4]
+hit.trajectory = { a: 2, b: -5, c: 4 }
+```
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