Minor improvements to docs (#105)

* Update model.jl

* Update manual.md

Author: raphaelsaavedra

docs/src/manual.md

@@ -1,5 +1,8 @@
 # Manual
 
+For a concise overview of the package, please read the [package paper](https://arxiv.org/abs/2008.05506). 
+It provides a high-level presentation of the theory behind score-driven models and showcases the features of the package as well as examples.
+
 ## Model Specification
 
 ```@docs

src/model.jl

@@ -59,7 +59,7 @@ end
 
 The constructor of a score-driven model. The model receives the lag structure, the 
 distribution and the scaling. You can define the lag structure in two different 
-ways, either by passing integers `p` and `q` to add all lags from `1` to `p and `1` to `q` or by 
+ways, either by passing integers `p` and `q` to add all lags from `1` to `p` and `1` to `q` or by 
 passing vectors of integers `ps` and `qs` containing the desired lags. Once you build 
 the model all of the unknown parameters that must be estimated are represented as `NaN`.