Add an example of using VSI (PDAL#4714)

* Add an example of using VSI

* Tune up the wording

Author: oleg-alexandrov

doc/VSI.md

@@ -0,0 +1,14 @@
+(VSI)=
+
+# VSI
+
+PDAL can read a file over a network, fetching only the portion that is needed for processing.
+
+Here is an example.
+
+```
+$ pdal info https://github.com/PDAL/data/raw/refs/heads/main/autzen/autzen-classified.copc.laz
+
+```
+
+This makes use of the [GDAL Virtual File Systems](https://gdal.org/en/stable/user/virtual_file_systems.html).

doc/stages/readers.md

@@ -2,13 +2,18 @@
 
 # Readers
 
+PDAL processes files in a variety of formats, listed below, with each
+tied to a reader.
+
 Readers provide {ref}`dimensions` to {ref}`pipeline`. PDAL attempts to
 normalize common dimension types, like X, Y, Z, or Intensity, which are often
 found in LiDAR point clouds. Not all dimension types need to be fixed, however.
 Database drivers typically return unstructured lists of dimensions.  A reader
 might provide a simple file type, like {ref}`readers.text`, a complex database
 like {ref}`readers.pgpointcloud`, or a network service like {ref}`readers.ept`.
 
+PDAL supports streaming a file from a remote server with {ref}`VSI`.
+
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