Fix notebook comment on how to use watch

[jorgearanda]

Fixes #45.

[codecov]

Codecov Report

Merging #46 into develop will decrease coverage by 0.15%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           develop      #46      +/-   ##
===========================================
- Coverage    93.69%   93.54%   -0.16%     
===========================================
  Files           26       26              
  Lines         1285     1285              
  Branches       274      274              
===========================================
- Hits          1204     1202       -2     
- Misses          45       46       +1     
- Partials        36       37       +1

Impacted Files	Coverage Δ
pyknow/matchers/rete/nodes.py	91.61% <0%> (-1.3%)	⬇️

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