Update installation instructions for spectratrait package

Author: serbinsh

README.md

@@ -38,20 +38,32 @@ Or 2) you can also run or source the "install_dependencies.R" script located in
 
 Finally, to complete the installation you will also need to install the spectratrait package itself.  You can do this by copying and pasting the command below into your R or RStudio (preferred) terminal.
 
+#### To install the main (default) branch version
 ``` r
-# to install the main (default) branch version
 devtools::install_github(repo = "plantphys/spectratrait", dependencies=TRUE)
+```
+<br>
 
-# to install the main branch version - with Vignettes (though slower)
+#### To install the main branch version - with Vignettes (though slower)
+``` r
 devtools::install_github(repo = "plantphys/spectratrait", dependencies=TRUE, build_vignettes = TRUE)
+```
+<br>
 
-# to install a specific release, for example release 1.0.5
+#### To install a specific release, for example release 1.0.5
+``` r
 devtools::install_github(repo = "plantphys/spectratrait@v1.0.5", dependencies=TRUE)
+```
+
+<br>
 
-# or a specific branch, e.g. a branch named devbranch
+#### Or install a specific branch, e.g. a branch named devbranch
+``` r
 devtools::install_github(repo = "plantphys/spectratrait", ref = "devbranch", dependencies=TRUE)
 ```
 
+<br>
+
 ## Contains:
 1. Core package functions are located in the in the main "R" folder
 2. inst/scripts contains example PLSR workflows for fitting example leaf and canopy spectra-trait PLSR models for different leaf traits, including LMA and foliar    nitrogen