ENH: Update release notes for release 7.2.0

RELEASE_NOTES.txt

-OTB-v 7.2.0 - Changes since version 7.1.0 (September 11th, 2020)
+OTB-v 7.2.0 - Changes since version 7.1.0 (October 02nd, 2020)
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 Features added:
@@ -35,6 +35,7 @@ CI:
 
 Documentation:
 
+   * !754: Fix spelling errors by Bas Couwenberg
    * !738: Update PSC informations by Julien Osman
    * !735: Correct menu instructions to open application-browser in Monteverdi by Julien Osman
    * !728: DOC: Deprecate methods that will be removed in OTB 8.0.0 by Julien Osman