Update readme

description

Update the readme (closes #47 (closed)):

• Reference the next paper.
• Include multi_tox() in examples.
• Add example plots and console output.

Other:

• Add "fnd" to roles of the UFZ.

system details

• R Version: 4.0.2
• RStudio Version: 1.3.1054
• OS Version: Windows 10 x64

checklist

• This merge introduces new features.
  • new features are documented
  • new features have tests
• update documentation including examples (if necessary)
• update and polish NEWS.md
• update version in DESCRIPTION
• update date in DESCRIPTION
• no remaining TODO, FIXME, or debug prints anywhere in the source files
• devtools::document() and commit the updated .Rd files
• devtools::check() without errors or warnings

README.md

 # stressaddition
-This R package makes it possible to model tri-phasic concentration-response relationships using the stress addition approach. It is useful for the analysis of ecotoxicological data where the traditional concentration addition or effect addition models are inadequate.
+This R package makes it possible to model tri-phasic concentration-response relationships using the stress addition approach. It is useful for the analysis of ecotoxicological data where the traditional concentration addition or effect addition models are inadequate. Its main functions are `ecxsys()` and `multi_tox()`.
 
-The `ecxsys()` function implements **EC<sub>x-SyS</sub>**, the tri-phasic concentration-response model introduced in
-[Liess, M., Henz, S. & Knillmann, S. Predicting low-concentration effects of pesticides. Sci Rep 9, 15248 (2019)](https://doi.org/10.1038/s41598-019-51645-4). It is applicable to modelling ecotoxicological experiments with and without environmental stress where the response displays a hormesis effect.
+`ecxsys()` implements **EC<sub>x-SyS</sub>**, the tri-phasic concentration-response model introduced in
+[Liess, M., Henz, S. & Knillmann, S. Predicting low-concentration effects of pesticides. Sci Rep 9, 15248 (2019)](https://doi.org/10.1038/s41598-019-51645-4). It is applicable to modelling ecotoxicological experiments with and without environmental stress where the response contains a hormesis effect.
 
-The `multi_tox()` function implements **Multi-TOX**, a model for binary mixtures of toxicants where each toxicant exhibits a tri-phasic concentration-response relationship. See *Liess, M., Henz, S., Shahid, N. (2020), Modelling the synergistic effects of toxicant mixtures. Manuscript submitted for publication*.
+`multi_tox()` implements **Multi-TOX**, a model for binary mixtures of toxicants where each toxicant exhibits a tri-phasic concentration-response relationship. See *Liess, M., Henz, S., Shahid, N. (2020), Modelling the synergistic effects of toxicant mixtures. Manuscript submitted for publication*.
 
-The EC<sub>x-SyS</sub> and Multi-TOX models are also available as part of the [Indicate app](http://www.systemecology.eu/indicate) which offers a graphical user interface.
+The EC<sub>x-SyS</sub> and Multi-TOX models are also available as part of the [Indicate app](http://www.systemecology.eu/indicate) which offers an easy to use graphical user interface.
 
 ## Installation
 This package is not yet available on CRAN. Until then you can install the most recent version from GitLab using the remotes package:
@@ -22,17 +22,20 @@ Please cite this package if you use it in your analysis. See `citation("stressad
 ## Examples
 
 ### EC<sub>x-SyS</sub>
-```r
+Model a concentration-response relationship with hormesis:
+```R
 library(stressaddition)
-
 model_a <- ecxsys(
     concentration = c(0, 0.05, 0.5, 5, 30),
     survival_tox_observed = c(90, 81, 92, 28, 0),
     survival_tox_env_observed = c(29, 27, 33, 5, 0),
     hormesis_concentration = 0.5
 )
+```
 
-# The LC50 under the influence of toxicant and system tress:
+Calculate the LC<sub>50</sub> and LC<sub>10</sub>:
+```R
+# LC50 under the influence of toxicant and system stress:
 lc(model_a, "survival_tox_sys", 50)
 # $response
 # [1] 44.95368
@@ -40,15 +43,17 @@ lc(model_a, "survival_tox_sys", 50)
 # $concentration
 # [1] 3.375735
 
-# The LC10 under the influence  of toxicant, system and environmental tress:
+# LC10 under the influence  of toxicant, environmental and system stress:
 lc(model_a, "survival_tox_env_sys", 10)
 # $response
 # [1] 26.41904
 # 
 # $concentration
 # [1] 0.0008571244
+```
 
-# Plot the survival and the stress:
+# Plot the survival and the stresses:
+```R
 par(mfrow = c(2, 1))
 plot_survival(model_a, show_legend = TRUE)
 plot_stress(model_a, show_legend = TRUE)
@@ -56,15 +61,13 @@ plot_stress(model_a, show_legend = TRUE)
 ![survival and stress plot](images/example.png)
 
 ### Multi-TOX
-```r
-# Define an additional single toxicant model:
+Define an additional single toxicant model and calculate the survival for some binary concentration mixtures:
+```R
 model_b <- ecxsys(
     concentration = c(0, 0.01, 0.1, 1, 10, 100),
     survival_tox_observed = c(96, 89, 91, 57, 9, 0),
     hormesis_concentration = 0.1
 )
-
-# Calculate the survival for some binary concentration mixtures:
 multi_tox(
     model_a,
     model_b,