Update README.md

README.md

-fitnd is a script which builds a modified version of the Numerical Recipes Levenberg–Marquardt algorithm
+_fitnd_ is a script which builds a modified version of the _Numerical Recipes_ Levenberg–Marquardt algorithm
 to fit data to a function, all specified on the command line.
 
-Before running, export the environment variable FITND_SRC to point to the directory where you have the fitnd script. 
+Before running, export the environment variable `FITND_SRC` to point to the directory where you have the fitnd script. 
 
 Help is given below. 
 
@@ -11,24 +11,26 @@ You can test that things work by running, from your cloned directory,
 fitnd "^+^*x0+^*x0*x0+^*x0*x0*x0" "test.dat"
 ``
 
-which should give you the output as in fit-test-cubic.png
+which should give you the output as in _fit-test-cubic.png_
 
-Requirements: cat, gcc, gnuplot, grep, nice, perl, sed, tail, wc 
+Requirements: _cat_, _gcc_, _gnuplot_, _grep_, _nice_, _perl_, _sed_, _tail_, _wc_ 
 
-For more help, run (from the FITND_SRC directory) fitnd without arguments. 
+For more help, run (from the `FITND_SRC` directory) fitnd without arguments. 
 
 
 
 --------------------------------------------------------------------
 
 
-fitnd
+_fitnd_
 
-Usage:
+**Usage:**
 
+``
 fitnd "function" filename [coefficients] [other options]
+``
 
-"function" should be in the form of a C-type function, with the letters a-q used as free parameters which you name, ^ is a free parameter (named automatically using r1,r2,r3 etc), s-z are dependent variables (you can use x0,x1,x2,... etc. as well). cos,sin,exp,tan,pow are treated explicitly and not turned into free parameters. ax is turned into (a*x), but don't try to rely on this too much - a properly formatted function is best! Remember this is C, so use pow(x,y) rather than x**y.
+"function" should be in the form of a C-type function, with the letters `a-q` used as free parameters which you name, `^` is a free parameter (named automatically using `r1`,`r2`,`r3` etc), `s-z` are dependent variables (you can use `x0`,`x1`,`x2`,... etc. as well). `cos`,`sin`,`exp`,`tan`,`pow` are treated explicitly and not turned into free parameters. `ax` is turned into `(a*x)`, but don't try to rely on this too much - a properly formatted function is best! Remember this is C, so use `pow(x,y)` rather than `x**y`.
 
 The filename is the name of the file that contains the data. This should be in space-separated columns.
 
@@ -39,61 +41,62 @@ Examples:
 ``
     fitnd "^+^*x0" file.dat
 ``
-     Fits file.dat, which contains <x,y> data, to a linear function.
+
+Fits file.dat, which contains `<x,y>` data, to a linear function.
 
 ``
-fitnd "^+^*x0*^x1" file2.dat 
+     fitnd "^+^*x0*^x1" file2.dat 
 ``
 
-     Fits file2.dat, which contains <x,y,z> data, to a function a+b*x*y.
+Fits file2.dat, which contains <x,y,z> data, to a function `a+b*x*y`.
 
 ``
-fitnd "^+exp(-0.5*pow((x0-^)/^,2.0)" file2.dat 1.0 2.0 3.0 
+     fitnd "^+exp(-0.5*pow((x0-^)/^,2.0)" file2.dat 1.0 2.0 3.0 
 ``
 
-     Gaussian fit, with vertical offset=1.0, mean=2.0 and variables=3.0.
+Gaussian fit, with vertical offset=1.0, mean=2.0 and variables=3.0.
 
-Optional arguments:
+**Optional arguments:**
 
-fixlow, fixhigh, fixends : these weight the ends of the data files so that they are effectively fixed. 
+`fixlow`, `fixhigh`, `fixends` : these weight the ends of the data files so that they are effectively fixed. 
 
-gnutype=... choose from lines, points, dots, etc. to fix the gnuplot line type
+`gnutype=...` choose from lines, points, dots, etc. to fix the _gnuplot_ line type
 
-nognu  - disables gnuplotting (useful for scripts/speed)
+`nognu`  - disables gnuplotting (useful for scripts/speed)
 
-extragnu="..." - any string given here is passed to gnuplot prior to the plot being made. Useful for scripting.
+`extragnu="..."` - any string given here is passed to gnuplot prior to the plot being made. Useful for scripting.
 
 (There are other arguments, but I cannot remember what they do :)
 
-PLEASE NOTE
+**PLEASE NOTE**
 
-The assumption is that your data have magnitudes AROUND 1.0 ... if you start using tiny
+The assumption is that your data have magnitudes _around_ 1.0 ... if you start using tiny
 numbers I humbly suggest that you multiply them to make them larger, and take this into account
 when making the fit, or use log space. Fitnd will not do this for you, learn to use
-sed, grep, gawk etc., or indeed Perl, instead.
+_sed_, _grep_, _gawk_ etc., or indeed `Perl`, instead.
 
 
 Relevant environment variables
 
-FITND_SRC
+`FITND_SRC`
 
 The location of the fitnd source files. Usually this is the directory which
 you cloned using git.
 
-FITND_GNUPLOT
+`FITND_GNUPLOT`
 
 The contents of this are sent to gnuplot before the fit function is plotted.
 
-FITND_COEFF_FORMAT
+`FITND_COEFF_FORMAT`
 
 This is the sprintf-style format specifier used to output coefficients. 
-Default is "%g".
+Default is `"%g"`.
 
-FITND_TMP
+`FITND_TMP`
 
 Temporary directory location. Default it "/tmp/".
 
-FITND_VB
+`FITND_VB`
 
 If set to "1" then verbose output is logged to the screen. Default is "0".