[change] Improve the generation performance of the result file and ad…

…ding some more information.

README.md

@@ -1,12 +1,25 @@
 # Primes
-List of primes, for more ressources : [https://primes.utm.edu/](https://primes.utm.edu/)
+List of the first 50 millions primes, for more ressources : [https://primes.utm.edu/](https://primes.utm.edu/).
 
 Source: [https://primes.utm.edu/lists/small/millions/](https://primes.utm.edu/lists/small/millions/)
 
-# Shell 
+# How to get the curated list ?
+
+These commands has been used on GNU/Linux (Ubuntu).
 ``` Shell
+# Download the 50 archives.
 curl -OL https://www.utm.edu/~caldwell/primes/millions/primes[1-50].zip
+# Unzip 
 find -maxdepth 1 -type f -name 'primes*.zip' -exec unzip {} \;
-for each in primes*.txt ; do awk 'NR>2 { for (i=1; i<=NF; i+=1) if ($i ~ /[0-9]+/ ) print($i) }' $each ; done | sort -h > primes.txt
+# Combine every text file in one file with one prime per line.
+for each in $(ls -1 primes*.txt| sort -t's' -n -k2) ; do awk 'NR>2 { for (i=1; i<=NF; i+=1) if ($i ~ /[0-9]+/ ) print($i) }' $each ; done > primes.txt
+# Check the result file
 sha256sum -c SHA256SUM.txt
+# Delete temporary files
+find -maxdepth 1 -type f \( -name 'primes*.zip' -or -name 'primes??.txt' -or -name 'primes?.txt' \) -delete
 ```
+
+# Use cases
+
+Solving some math problems from [https://projecteuler.net/](https://projecteuler.net/), has been easier with a precomputed list of primes.
+