add descriptions of reading and writing options

src/uproot/reading.py

@@ -82,7 +82,8 @@ def open(
     Options (type; default):
 
     * handler (:doc:`uproot.source.chunk.Source` class; None)
-    * timeout (float for HTTP, int for XRootD; 30)
+    * timeout (float for HTTP, int for XRootD, ignored for other sources; 30)
+        The time in seconds to wait before giving up on the connection.
     * max_num_elements (None or int; None)
         The maximum number of elements to be requested in a single vector read, when using XRootD.
     * num_workers (int; 1)
@@ -526,14 +527,22 @@ class ReadOnlyFile(CommonFileMethods):
     Options (type; default):
 
     * handler (:doc:`uproot.source.chunk.Source` class; None)
+        Class implementing reading from the data source.
+        If None, deduced from input file type.
     * timeout (float for HTTP, int for XRootD; 30)
+        The time in seconds to wait before giving up on the connection.
+        Ignored for non-internet sources like local file paths.
     * max_num_elements (None or int; None)
        The maximum number of elements to be requested in a single vector read, when using XRootD.
     * num_workers (int; 1)
+        Number of tasks to spawn for reading and decompression.
     * use_threads (bool; False on the emscripten platform (i.e. in a web browser), else True)
+        Use multi-threading when spawning workers.
     * num_fallback_workers (int; 10)
     * begin_chunk_size (memory_size; 403, the smallest a ROOT file can be)
+        Size of first chunk that we attempt to read in bytes.
     * minimal_ttree_metadata (bool; True)
+        Defer the reading of metadata until they are accessed.
 
     See the `ROOT TFile documentation <https://root.cern.ch/doc/master/classTFile.html>`__
     for a specification of ``TFile`` header fields.