Trivial typo fix

Your spellcheck missed it.
+ updated spelling.dat to catch it next time

scripts/spell_check/spelling.dat

@@ -5540,6 +5540,7 @@ pususading:persuading
 puting:putting:*
 pwoer:power
 pyscic:psychic
+pythin:python
 qgsi:qgis
 qoute:quote
 qouted:quoted

src/app/pluginmanager/README

@@ -32,7 +32,7 @@ downloads           number of downloads
 average_vote        average vote
 rating_votes        number of votes
 
-* status is only obligatory for Pythin plugins and it must match all the tags:
+* status is only obligatory for Python plugins and it must match all the tags:
 available, installed. version_available, version_installed.
 orphan = installed and not available to download;
 new = not installed and seen for the first time;