added comm documentation

_commands/tools/comm.md

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+---
+---
+
+comm
+-------
+
+comm is used to compare two text files, sorted lexically(alphabetically), by printing 
+three columns of mutually exclusive output:
+Column 1: Lines only in file 1
+Column 2: Lines only in file 2
+Column 3: Lines common to both files
+
+~~~ bash
+comm file1 file2
+~~~
+
+
+### Useful Options / Examples
+There are 4 optional tags for comm:
++ "-1" supresses printing column 1
++ "-2" supresses printing column 2
++ "-3" supresses printing column 3
++ "-i" ignores case, so "apple" and "Apple" are treaed as identical
+
+
+#### Example command
+```
+cat file1
+2
+3
+4
+5
+7
+9
+
+cat file2
+1
+2
+4
+6
+
+comm file1 file 2
+        1
+                2
+3
+				 4
+5
+        6
+7 
+9
+```
+##### Break it down
+In the above example, we can see that the left column contains the items only in file1,
+the middle column contains only items in file2, and the right column contains items
+appearing in both files