doc/config.rst: Fix some typos

doc/config.rst

@@ -2,7 +2,7 @@
 The Config System
 #################
 
-*imSim* utilizes the *imSim* config system to configure itself.  This choice was made for several reasons.  As *GalSim* is used to render the actual images, using *GalSim* itself is a natural choice for configuration. Perhaps most importantly, by implementing the *imSim* code as a *GalSim* module it becomes possible to use it freely with other *GalSim* based modules.  So, other programs in the *GalSim* ecosystem can also call and configure the *imSim* module and could (for example) utilize the *imSim* electronics readout algorithms as part of their functionality.
+*imSim* utilizes the *GalSim* config system to configure itself.  This choice was made for several reasons.  As *GalSim* is used to render the actual images, using *GalSim* itself is a natural choice for configuration. Perhaps most importantly, by implementing the *imSim* code as a *GalSim* module it becomes possible to use it freely with other *GalSim* based modules.  So, other programs in the *GalSim* ecosystem can also call and configure the *imSim* module and could (for example) utilize the *imSim* electronics readout algorithms as part of their functionality.
 
 The *GalSim* config system is described in the `GalSim documentation <http://galsim-developers.github.io/GalSim/_build/html/config.html>`__. You should start there to understand the basic functionality of the config system.  If you look at the ``config/imsim-config.yaml`` distributed with *imSim* you can see the *imSim's* default configuration.  When you read in a YAML file you will be adding to and modifying these results.
 
@@ -47,7 +47,7 @@ These classes define the user configurable parts of the ``input`` section of the
 Instance catalogs
 -----------------
 
-Instance catalogs are text files best suited to making small handcrafted inputs. For legacy and compatibility purposes, They follow the format of the *PhoSim* program inputs which are documented on `PhoSim Web Site <https://bitbucket.org/phosim/phosim_release/wiki/Instance%20Catalog>`__.  The file should contain a a header including metadata describing the observation and a list of sources.
+Instance catalogs are text files best suited to making small handcrafted inputs. For legacy and compatibility purposes, they follow the format of the *PhoSim* program inputs which are documented on `PhoSim Web Site <https://bitbucket.org/phosim/phosim_release/wiki/Instance%20Catalog>`__.  The file should contain a a header including metadata describing the observation and a list of sources.
 
 Key Name: instance_catalog
 ^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -112,7 +112,7 @@ Optional keywords to set:
 Sky Catalogs
 ------------
 
-Instance catalogs are text based and utilize a lot of disk space for the information contained in them. Also, one instance catalog is needed for each visit, even if those visits take place at the exact same position on the sky.  This causes enormous duplication of information.  Instead, large area simulations, *imSim* utilizes an API based system known as `skyCatalogs <https://github.com/LSSTDESC/skyCatalogs>`__.  The *skyCatalog* presents a unified interface to *imSim* via an API of databases that contain all of the object in the sky.  By configuring *imSim* to use the *skyCatalog* API only metadata for the visits are needed.  *imSim* will retrieve a list of all of the objects it needs to render through the interface.  *skyCatalogs* can contain static and transient information and databases exist both for synthetic skies and true sources of information such as the Gaia catalog.  The *skyCatalog* can also serve as a source of truth information when later analyzing simulated data.
+Instance catalogs are text based and utilize a lot of disk space for the information contained in them. Also, one instance catalog is needed for each visit, even if those visits take place at the exact same position on the sky.  This causes enormous duplication of information.  Instead, for large area simulations, *imSim* utilizes an API based system known as `skyCatalogs <https://github.com/LSSTDESC/skyCatalogs>`__.  The *skyCatalog* presents a unified interface to *imSim* via an API of databases that contain all of the object in the sky.  By configuring *imSim* to use the *skyCatalog* API only metadata for the visits are needed.  *imSim* will retrieve a list of all of the objects it needs to render through the interface.  *skyCatalogs* can contain static and transient information and databases exist both for synthetic skies and true sources of information such as the Gaia catalog.  The *skyCatalog* can also serve as a source of truth information when later analyzing simulated data.
 
 Key Name: sky_catalog
 ^^^^^^^^^^^^^^^^^^^^^