Add initial documentation for all implemented networks.

Author: mitkonikov

Diff for: README.md

@@ -1,7 +1,7 @@
 # Forward-Forward Neural Networks Library
 
-FFLib is a neural network library based on PyTorch that aims to implement
-several different types of layers and networks based on the Forward-Forward algorithm.
+FFLib is a neural network library based on PyTorch [2] that aims to implement
+several different types of layers and networks based on the Forward-Forward algorithm [1].
 The library also provides a suite of tools for training, validating, testing, debugging and experimenting
 with Forward-Forward-based networks. We aim to make this library as close as possible
 to the original design and structure of the PyTorch library.
@@ -31,7 +31,7 @@ and making interactive execution only afterwards.
 
 The Forward-Forward Algorithm was introduced in Geoffrey Hinton's paper
 ["The Forward-Forward Algorithm: Some Preliminary Investigations"](https://arxiv.org/abs/2212.13345)
-with the following abstract:
+[1] with the following abstract:
 
 ```
 The aim of this paper is to introduce a new learning procedure for neural networks and to
@@ -48,6 +48,50 @@ in the positive pass and allow video to be pipelined through the network without
 storing activities or stopping to propagate derivatives.
 ```
 
+## Types of FF Networks
+
+There are 3 different types of Forward-Forward-based Neural Networks implemented in the FFLib:
+ - [**FFNet**](#ffnet) - [example usage](./examples/ff_net_mnist.py)
+ - [**FF+C**](#ffc) - [example usage](./examples/ff_c_mnist.py)
+ - [**FFRNN**](#ffrnn) - [example usage](./examples/ff_rnn_mnist.py)
+
+### FFNet
+
+The basic example of a Neural Network based on the Forward-Forward Algorithm.
+In the example file the following network specifications are used:
+ - 2 Dense layers with 2000 neurons each
+ - Predicting the MNIST dataset with TryAll probe
+ - Batch Size of 128
+
+When a dense layer accepts an input, it is first detached from the graph
+and normalized before applying the weight multiplication.
+Essentially, it's just a linear layer that gets a detached normalized input.
+The trick is that each layer optimizes its "goodness"
+to be positive for "positive" data and negative for "negative" data.
+In the case of FFNet, the input and output has to be combined
+and given as an input to the network (to the first layer).
+Since there's no output of the network, we have to try all inputs when predicting.
+In the FFLib, there are special classes called [probes](./src/fflib/probes/__init__.py).
+We use the [TryAll probe](./src/fflib/probes/one_hot.py) to try all possible one-hot labels.
+
+### FF+C
+
+FF+C is a type of hybrid Neural Network that uses both, the Forward-Forward Algorithm
+and ordinary backpropagation to avoid the need ot the TryAll probe.
+The FF part is used as a feature extractor and it is trained the same way as the original FF network.
+The Classifier is another dense layer that as input gets the
+concatenated activations from both of the FF Dense layers and tries to predict the one-hot label.
+
+### FFRNN
+
+The Forward-Forward Recurrent Neural Network is the most complex type of FF network implemented
+in the FFLib. It is made of a special type of layer called [FFRecurrentLayer](./src/fflib/nn/ff_recurrent_layer.py).
+The example file contains an example usage of the FFRNN with 2 FF Recurrent Layers, both with 2000 neurons.
+These networks are quite large due to the fact that each layer has not only weights
+from the previous layer, but also backward weights from the next layer.
+These networks have to be trained with multiple frames per batch, thus
+requiring even more time for both, training and inference.
+
 ## Contributions
 
 We really appreciate contributions from the community!
@@ -91,6 +135,8 @@ We also recommend installing the VSCode extension
 [GitHub Local Actions](https://marketplace.visualstudio.com/items?itemName=SanjulaGanepola.github-local-actions)
 to run the workflows from inside VSCode, making the process painless.
 
+Example scenarios are also tested in GitHub Actions by running them from the CLI.
+
 ## General Guidelines
 
 Here are a few guidelines to following while contributing on the library:
@@ -100,3 +146,8 @@ Here are a few guidelines to following while contributing on the library:
  - Strict formatting style guidelines using `black`
  - No recursion (at our abstraction level)
  - Nicely documented functions and classes
+
+## References
+
+ - [**[1]**](https://arxiv.org/abs/2212.13345) - Hinton, G. (2022). The Forward-Forward Algorithm: Some preliminary investigations.
+ - [**[2]**](https://pytorch.org/) - PyTorch.