Update README.md (#105)

* Update README.md

adds estimate-area documentation

Author: Allison Zheng

README.md

@@ -42,6 +42,7 @@ export MAPBOX_ACCESS_TOKEN=my.token
   * [`view-source`](#view-source)
   * [`list-sources`](#list-source)
   * [`delete-source`](#delete-source)
+  * [`estimate-area`](#estimate-area)
 * Recipes
   * [`view-recipe`](#view-recipe)
   * [`validate-recipe`](#validate-recipe)
@@ -150,6 +151,41 @@ tilesets delete-source
 
 Permanently delete a tileset source and all of its files. This is not a recoverable action!
 
+### estimate-area 
+
+```shell
+tilesets estimate-area <features> -p/--precision <precision>
+```
+
+Estimates tiled area (km<sup>2</sup>) of features with a specified precision. Accepts line-delimited GeoJSON or GeoJSON feature collections as files or via `stdin` or a list of string-encoded coordinate pairs of the form "[lng, lat]", or "lng, lat", or "lng lat". Precision must be 10m, 1m, 30cm or 1cm.
+
+Flags:
+
+* `-p` or `--precision` [required]: precision level
+* `--no-validation` [optional]: do not validate source data locally before area calculation
+* `--force-1cm` [optional]: the --force-1cm flag must be present to enable 1cm precision area calculation and may take longer for large feature inputs or data with global extents. 1cm precision for tileset processing is only available upon request after contacting [Mapbox support](https://support.mapbox.com/hc/en-us/requests/new?ticket_form_id=360000291231)
+
+Usage
+
+```shell
+
+# GeoJSON feature files
+tilesets estimate-area ./file1.geojson ./file2.geojson -p <precision>
+
+# GeoJSON features in stdin redirection 1
+tilesets estimate-area -p <precision> < ./file.geojson
+
+# GeoJSON features in stdin redirection 2
+cat ./file.geojson | tilesets estimate-area -p <precision>
+
+# GeoJSON features in stdin stream 
+tilesets estimate-area --precision <precision>
+<features>  
+
+# coordinate pairs (must be in quotes)
+tilesets estimate-area "[lng,lat]" "[lng,lat]" --precision <precision>
+```
+
 ### view-recipe
 
 Prints the Recipe JSON to stdout.