docs: User M-Codes - fix typo

Author: andypugh

docs/src/gcode/m-code.txt

@@ -710,7 +710,7 @@ M1-- <P- Q->
 After creating a new 'M1nn' file you must restart the GUI so it is aware
 of the new file, otherwise you will get an 'Unkown m code' error.
 
-The external program named 'M100' through 'M199' (no extension and a capitol M)
+The external program named 'M100' through 'M199' (no extension and a capital M)
 is executed with the optional P and Q values as its two arguments.
 Execution of the G code file pauses until the external program exits.
 Any valid executable file can be used. The file must be located in the search
@@ -720,15 +720,15 @@ path specificed in the ini file configuration. See the
 [WARNING]
 Do not use a word processor to create or edit the files. A word processor
 will leave unseen codes that will cause problems and may prevent a bash or
-python file from working. Use a text editor like Gedit in Ubuntu or Notepad++
+python file from working. Use a text editor like Geany in Debian or Notepad++
 in other operating systems to create or edit the files.
 
 The error 'Unknown M code used' denotes one of the following
 
 * The specified User Defined Command does not exist
 * The file is not an executable file
 * The file name has an extension
-* The file name does not follow this format M1nn where nn = 00 through 99
+* The file name does not follow this format Mnnn where nnn = 100 through 199
 * The file name used a lower case M
 
 For example to open and close a collet closer that is controlled by a