Change alt/orig to build/to use heading levels

As the 'Alternate code' and 'Original code' heading level is now 2 the
'To build' and 'To use' subsections should be level 3, not 4, and also
reworded, this was done:

    sgit -e 's/^#### To build/### Alternate build/g' -e 's/^#### To use/### Alternate use/g' '*README.md'

Many more have to be updated and this will be done manually at another
time.

1984/anonymous/README.md

@@ -21,13 +21,13 @@ in order to show the code that was turned into the
 [tattoo](https://web.archive.org/web/20070120220721/https://thomasscovell.com/tattoo.php),
 as the alternate code. See below in the tattoo side-by-side with the code.
 
-#### To build:
+### Alternate build:
 
 ```sh
 make alt
 ```
 
-#### To use:
+### Alternate use:
 
 NOTE: this version might not work on some systems like macOS.
 

1984/decot/README.md

@@ -20,13 +20,13 @@ This alternate code, the original, requires a compiler that supports
 `-traditional-cpp` or an old enough compiler. If you have such a compiler you
 can use this entry.
 
-#### To build:
+### Alternate build:
 
 ```sh
 make alt
 ```
 
-#### To use:
+### Alternate use:
 
 ```sh
 ./decot.alt

1984/mullender/README.md

@@ -34,7 +34,7 @@ as it goes so fast in modern systems. The author suggested that there was a
 delay in the original code as well.
 
 
-#### To build:
+### Alternate build:
 
 
 ```sh
@@ -42,7 +42,7 @@ make alt
 ```
 
 
-#### To use:
+### Alternate use:
 
 ```sh
 ./mullender.alt [microseconds]
@@ -122,7 +122,7 @@ close to as the original as possible we used a copy of
 in the *fabulous* [Unix History
 Repo](https://github.com/dspinellis/unix-history-repo/tree/Research-Release).
 
-#### To build:
+### Alternate build:
 
 `gentab.c` can be built like:
 
@@ -131,7 +131,7 @@ Repo](https://github.com/dspinellis/unix-history-repo/tree/Research-Release).
 make gentab
 ```
 
-#### To use:
+### Alternate use:
 
 ```sh
 ./gentab file