Add --product option's documentation, and note for sentinel data users

README.md

@@ -77,14 +77,16 @@ Options:
  -l command
 
  -l, --location-name TEXT Location name in string format
- -p, --pan-enhancement Enhance image with panchromatic band
- --no-preview Skip downloading of preview image
+ -pan, --pan-enhancement Enhance image with panchromatic band
+ --no-preview Skip previewing of pre-processed low resolution RGB
+ satellite image.
+
  -v, --vegetation Show Color Infrared image to highlight
  vegetation
 
  -V, --version Show the version number and quit
+ -p, --product TEXT Product name 'landsat'/'sentinel'
  --help Show this message and exit.
-
 ```
 
 Felicette can download and process Landsat images taking the location's input as `(lon, lat)` or the location name. They can be used in the following way.
@@ -97,10 +99,17 @@ With coordinates:
 
  $ felicette -c 77.5385 8.0883
 
-`-p` option uses the panchromatic band to enhance image's resolution to 15 meters, contrary to resolution of RGB bands(30 meters). 
-To get a better image using felicette use:
+`--product` / `-p` option is used to specify which data-product is used to generate images i.e Sentinel or Landsat. By default, Landsat-8 data will be used to generate images.
+
+ $ felicette -l "Kanyakumari" -p "sentinel"
+
+**NB**: *To use sentinel data source, one has to set `AWS_ACCESS_KEY_ID` and `AWS_SECRET_ACCESS_KEY` (To generate a pair, go to AWS console -> My Security Credentials -> Access keys). This is because [Sentinel-2 data](https://registry.opendata.aws/sentinel-2/) is in a [Requester Pays](https://docs.aws.amazon.com/AmazonS3/latest/dev/RequesterPaysBuckets.html) bucket.
+
+
+`-pan` option uses the panchromatic band to enhance image's resolution to 15 meters, contrary to resolution of RGB bands(30 meters) if Landsat product is being used. Felicette doesn't support any panchromatic enhancements for Sentinel-2 data which already have a resolution of 10m.
+To get a better Landsat image using felicette use:
 
- $ felicette -p -c 77.5385 8.0883
+ $ felicette -pan -c 77.5385 8.0883
 
 `--no-preview` option doesn't download image to preview, and directly downloads and processes original data. Please use this if you're sure of the location/quality of the images to be generated by felicette with the arguments provided to it.