Customize nano behavior. Use ~/.nanorc file.

nanorc

#####################
# Behavior Settings #
#####################

# Make new lines contain the same amount of whitespace as line above.
unset autoindent

# Use a tab size of n columns. The value of n must be greater than 0.
# The default value is 8.
set tabsize 4

# Convert typed tabs to spaces.
set tabstospaces

# Do not convert files from DOS/Mac format.
unset noconvert

# Add newlines to the ends of files.
unset nonewlines

# Make the Home key smarter. When Home is pressed anywhere but at the very
# beginning of non-whitespace characters on a line, the cursor will jump to that
# beginning (either forwards or backwards). If the cursor is already at that
# position, it will jump to the true beginning of the line.
set smarthome

####################
# Display Settings #
####################

# Constantly display the cursor position in the status bar.
# Constantly display the cursor position in the status bar. This overrides the option quickblank.
set constantshow

# Display line numbers to the left of the text area.
set linenumbers

# Use the blank line below the titlebar as extra editing space.
set morespace

# Use smooth scrolling by default.
set smooth

# Disable soft line wrapping for easier viewing of very long lines.
unset softwrap

#######################
# Syntax Highlighting #
#######################

include "/usr/share/nano/Dockerfile.nanorc"
include "/usr/share/nano/asm.nanorc"
include "/usr/share/nano/autoconf.nanorc"
include "/usr/share/nano/awk.nanorc"
include "/usr/share/nano/c.nanorc"
include "/usr/share/nano/changelog.nanorc"
include "/usr/share/nano/cmake.nanorc"
include "/usr/share/nano/css.nanorc"
include "/usr/share/nano/debian.nanorc"
include "/usr/share/nano/default.nanorc"
include "/usr/share/nano/elisp.nanorc"
include "/usr/share/nano/fortran.nanorc"
include "/usr/share/nano/gentoo.nanorc"
include "/usr/share/nano/go.nanorc"
include "/usr/share/nano/groff.nanorc"
include "/usr/share/nano/guile.nanorc"
include "/usr/share/nano/html.nanorc"
include "/usr/share/nano/java.nanorc"
include "/usr/share/nano/javascript.nanorc"
include "/usr/share/nano/json.nanorc"
include "/usr/share/nano/lua.nanorc"
include "/usr/share/nano/makefile.nanorc"
include "/usr/share/nano/man.nanorc"
include "/usr/share/nano/mgp.nanorc"
include "/usr/share/nano/mutt.nanorc"
include "/usr/share/nano/nanorc.nanorc"
include "/usr/share/nano/nftables.nanorc"
include "/usr/share/nano/objc.nanorc"
include "/usr/share/nano/ocaml.nanorc"
include "/usr/share/nano/patch.nanorc"
include "/usr/share/nano/perl.nanorc"
include "/usr/share/nano/php.nanorc"
include "/usr/share/nano/po.nanorc"
include "/usr/share/nano/postgresql.nanorc"
include "/usr/share/nano/pov.nanorc"
include "/usr/share/nano/python.nanorc"
include "/usr/share/nano/ruby.nanorc"
include "/usr/share/nano/sh.nanorc"
include "/usr/share/nano/spec.nanorc"
include "/usr/share/nano/tcl.nanorc"
include "/usr/share/nano/tex.nanorc"
include "/usr/share/nano/texinfo.nanorc"
include "/usr/share/nano/xml.nanorc"

Why not include "/usr/share/nano/*.nanorc" ?