Hotlink bioRad figure to reduce pkg size #376

Reduces package size to 4.5MB on R CMD build bioRad

devtools::build() still has a note on package being to large

Author: peterdesmet

docs/dev/articles/bioRad.html

@@ -51,7 +51,7 @@ The underlying C-code for the algorithm has been refactored for compatibility wi
 
 ## Figure 2
 
-![**Figure 2 from [Dokter et al. (2019)][dokter_2019]**](ecog12354-fig-0002-m.jpg)
+![**Figure 2 from [Dokter et al. (2019)][dokter_2019]**](https://onlinelibrary.wiley.com/cms/asset/5ffef211-85c6-4610-9d4c-0b7063e4b144/ecog12354-fig-0002-m.jpg)
 
 The figure shows the structure and interrelation of bioRad's main class objects, functions, and plotting methods. (A) **objects** (rounded box), **functions** (`fixed width font`) and their **relation** (arrows). (B–K) output of the default plot methods for a European radar (left row, Offenthal radar, Germany, 2016-10-04 15:15 UTC–2016-10-05 08:45 UTC) and US radar (right row, KBRO radar, Texas, 2017-05-14 00:09 UTC–2017-05-14 13:25 UTC). The dotted line in (H) and (K) indicates the time slice of (B), (D), (F) and (C), (E), (J) respectively. Grey shading indicates night time (time on the x-axis is in UTC). Altitudes are relative to mean sea level.