git-rm(1): Remove files from working tree/from ...

NAME

<file>Files to remove from the index and optionally, from the working tree as well.
-f: Remove files from the working tree as well as from the index.
-n: Don't actually remove the file(s), just show if they exist in the index.
-v: Be verbose.
--: This option can be used to separate command-line options from the list of files, (useful when filenames might be mistaken for command-line options).

1.: You can put the name of a directory on the command line, and the command will remove all files in it and its subdirectories (the directories themselves are never removed from the working tree);
2.: Giving the name of a file that is not in the index does not remove that file.

git-rm Documentation/\*.txt: Removes all *.txt files from the index that are under the Documentation directory and any of its subdirectories. The files are not removed from the working tree.
Note that the asterisk * is quoted from the shell in this example; this lets the command include the files from subdirectories of Documentation/ directory.
git-rm -f git-*.sh: Remove all git-*.sh scripts that are in the index. The files are removed from the index, and (because of the -f option), from the working tree as well. Because this example lets the shell expand the asterisk (i.e. you are listing the files explicitly), it does not remove subdir/git-foo.sh.