README.md and Makefile update.

Makefile

@@ -7,3 +7,6 @@ clean:
 install:
 	cp ./checkpw /usr/bin/
 
+uninstall:
+	rm -f /usr/bin/checkpw
+

README.md

@@ -4,10 +4,14 @@ checkpw is a program that checks the validity of a users password on a Linux/PAM
 
 ## The idea behind:
 
+I needed a program to verify passwords of users on Linux based systems using PAM.
+
 Exactly a program like this... not more!
 
 # Installation:
 
+**WARNING:** Install this software with care. checkpw could easily be used for bruteforcing passwords from local users!
+
 ```
 git clone https://git.xw3.org/hanez/checkpw.git
 cd checkpw
@@ -15,6 +19,15 @@ make
 sudo make install
 ```
 
+The code only supports verifying passwords for user id 1000 by default. Look a the code for some compile time options!
+
+Set MAX_UID and MIN_UID in the code or you can compile checkpw without editing the code using the following command and install it manually:
+
+```
+gcc -Werror -lpam -lpam_misc -DMAX_UID=1000 -DMIN_UID=1000 -o checkpw checkpw.c
+sudo cp ./checkpw /usr/bin/
+```
+
 # Usage:
 
 ```