Added Readme notes for TkCanvas backend

Author: josepegea

Diff for: README.md

@@ -5,7 +5,26 @@ An advanced plotting library for Ruby.
 
 It aims to allow you to visualize anything, anywhere with a flexible, extensible, Ruby-like API.
 
-# Usage
+# Backends
+
+Rubyplot can use different backends to render its plots:
+
+- `magick` Using ImageMagick
+- `gr` Using the GR framework
+- `tk_canvas` Interactive drawing in a Canvas object using Ruby/Tk
+
+Call `Rubyplot.set_backend` at the start of your program to select
+the desired backend.
+
+Pick the desired one:
+
+``` ruby
+Rubyplot.set_backend(:magick)
+Rubyplot.set_backend(:gr)
+Rubyplot.set_backend(:tk_canvas)
+```
+
+# Installing GR
 
 Install the GR framework from the [website](https://gr-framework.org/c.html).
 
@@ -17,6 +36,25 @@ export GKS_FONTPATH="/home/sameer/Downloads/gr"
 export RUBYPLOT_BACKEND="GR"
 ```
 
+# Installing Tk
+
+In addition to install the `tk` gem in your project, you need to
+install the Tcl/Tk runtime in your system. The instructions depending
+on the OS but it is a safe bet to install the Community Edition of
+Active Tcl from https://www.activestate.com/
+
+You have more details about installing Tk in different systems in the
+excelent [TkDocs](https://tkdocs.com/tutorial/install.html) website.
+
+If you want to have a more modern way of interacting with Tk from
+Ruby, you can use
+[TkComponent](https://github.com/josepegea/tk_component) and
+[TkInspect](https://github.com/josepegea/tk_inspect).
+
+# Examples
+
+See the [examples](./examples) to see some how-to code.
+
 # Short term priorities
 
 Check milestones in GitHub for more information.

Diff for: examples/tk_canvas_wrapper/README.md

@@ -6,4 +6,4 @@ using the TkCanvasWrapper.
 ## Running
 
     bundle exec tk_plot_demo.rb
-    
+

Diff for: rubyplot.gemspec

@@ -8,7 +8,7 @@ Rubyplot::DESCRIPTION = "An advanced plotting library for Ruby."
 Gem::Specification.new do |spec|
   spec.name          = 'rubyplot'
   spec.version       = Rubyplot::VERSION
-  spec.authors       = ['Arafat Khan', 'Pranav Garg', 'John Woods', 'Pjotr Prins', 'Sameer Deshmukh']
+  spec.authors       = ['Arafat Khan', 'Pranav Garg', 'John Woods', 'Pjotr Prins', 'Sameer Deshmukh', 'Josep Egea']
   spec.email         = ['[email protected]'] # add other author ids 
   spec.summary       = %q{An advaced plotting library for Ruby.}
   spec.description   = Rubyplot::DESCRIPTION