Correct small typos in changes and usage

docs/changes.rst

@@ -161,7 +161,7 @@ Other changes:
 
 - improve file size displays, more flexible size formatters
 - explicitly commit to the units standard, #289
-- archiver: add E status (means that an error occured when processing this
+- archiver: add E status (means that an error occurred when processing this
   (single) item
 - do binary releases via "github releases", closes #214
 - create: use -x and --one-file-system (was: --do-not-cross-mountpoints), #296

docs/usage.rst

@@ -441,7 +441,7 @@ Miscellaneous Help
 
 Debug Commands
 --------------
-There are some more commands (all starting with "debug-") wich are are all
+There are some more commands (all starting with "debug-") which are all
 **not intended for normal use** and **potentially very dangerous** if used incorrectly.
 
 They exist to improve debugging capabilities without direct system access, e.g.